Evan,

I tested the new build and I didn't encounter any problems with "try ubuntu" or "install ubuntu" keys (tested several times). I did find another bug which I can reproduce
each time (even in debugmode!). I you happen to click the "red cross" of the dialog (
be it by accident or intentionally, as I did) a new dialog pops up "Do you really want to quit the installation now?". If you click the cancel button, then system hangs. 

I tried this condition in the debug-mode (start terminal, enter ubiquity -d). I dumped
the contents of the file /var/log/installer/debug at the end of the comment (apport
gave a problem) 

Unfortunately 
the call apport-collect 539827 yields the following message: 

ubuntu@ubuntu:~$ apport-collect 539827
The authorization page:
   (https://edge.launchpad.net/+authorize-token?oauth_token=Q3qNdqbldTDHCQhMNVZq&allow_permission=WRITE_PRIVATE)
should be opening in your browser. After you have authorized
this program to access Launchpad on your behalf you should come
back here and press <Enter> to finish the authentication process.

Error connecting to Launchpad: 
You can reset the credentials by removing the file "/home/ubuntu/.cache/apport/launchpad.credentials"
ubuntu@ubuntu:~$ rm /home/ubuntu/.cache/apport/launchpad.credentials
rm: cannot remove `/home/ubuntu/.cache/apport/launchpad.credentials': No such file or directory
ubuntu@ubuntu:~$ 

---
cat /var/log/installer/debug 
Ubiquity 2.2.8
/usr/lib/ubiquity/ubiquity/frontend/gtk_ui.py:553: GtkWarning: gtk_window_resize: assertion `width > 0' failed
  widget.resize(w, h)
/usr/lib/ubiquity/ubiquity/frontend/gtk_ui.py:729: GtkWarning: gtk_widget_realize: assertion `GTK_WIDGET_ANCHORED (widget) || GTK_IS_INVISIBLE (widget)' failed
  widget.realize()
/usr/lib/ubiquity/ubiquity/frontend/gtk_ui.py:722: Warning: g_object_get_qdata: assertion `G_IS_OBJECT (object)' failed
  unused = widget.get_image()
/usr/lib/ubiquity/ubiquity/frontend/gtk_ui.py:722: Warning: g_type_get_qdata: assertion `node != NULL' failed
  unused = widget.get_image()
Ubiquity 2.2.8
debconf (developer): <-- VERSION 2
debconf (developer): --> 0 2.0
debconf (developer): <-- CAPB 
debconf (developer): --> 0 multiselect escape 
debconf (developer): <-- GET oem-config/enable
debconf (developer): --> 10 oem-config/enable doesn't exist
debconf (developer): <-- GET ubiquity/automation_failure_command
debconf (developer): --> 0 
debconf (developer): <-- GET ubiquity/failure_command
debconf (developer): --> 0 
debconf (developer): <-- GET ubiquity/success_command
debconf (developer): --> 0 
debconf (developer): <-- GET debian-installer/locale
debconf (developer): --> 0 
debconf (developer): <-- GET debian-installer/fallbacklocale
debconf (developer): --> 0 
/usr/lib/ubiquity/ubiquity/frontend/gtk_ui.py:553: GtkWarning: gtk_window_resize: assertion `width > 0' failed
  widget.resize(w, h)
debconf (developer): <-- VERSION 2
debconf (developer): --> 0 2.0
debconf (developer): <-- CAPB 
debconf (developer): --> 0 multiselect escape 
debconf (developer): <-- FSET localechooser/languagelist seen false
debconf (developer): --> 0 false
debconf (developer): <-- GET ubiquity/show_alpha_warning
debconf (developer): --> 0 false
Mar 26 07:16:37 ubiquity: Starting up '['log-output', '-t', 'ubiquity', '--pass-stdout', '/usr/lib/ubiquity/localechooser/localechooser']' for ubi-language.Page
Mar 26 07:16:37 ubiquity: Watching for question patterns localechooser/languagelist
debconf (developer): <-- CAPB escape
debconf (developer): --> 0 multiselect escape 
Mar 26 07:16:37 debconf (filter): <-- CAPB backup
debconf (developer): <-- CAPB backup escape
debconf (developer): --> 0 multiselect escape 
Mar 26 07:16:37 debconf (filter): <-- REGISTER debian-installer/language debconf/language
debconf (developer): <-- REGISTER debian-installer/language debconf/language
debconf (developer): --> 0
Mar 26 07:16:37 debconf (filter): <-- FGET localechooser/languagelist seen
debconf (developer): <-- FGET localechooser/languagelist seen
debconf (developer): --> 0 false
Mar 26 07:16:40 debconf (filter): <-- SUBST localechooser/languagelist CODES C, sq, am, ar, ast, eu, be, bn, bs, bg, ca, zh_CN, zh_TW, hr, cs, da, nl, dz, en, eo, et, fi, fr, gl, ka, de, el, gu, he, hi, hu, id, ga, it, ja, kk, km, ko, ku, lv, lt, mk, ml, mr, ne, se_NO, nb_NO, nn_NO, pl, pt, pt_BR, pa, ro, ru, sr, sk, sl, es, sv, tl, ta, th, tr, uk, vi, cy, wo
debconf (developer): <-- SUBST localechooser/languagelist CODES C,\ sq,\ am,\ ar,\ ast,\ eu,\ be,\ bn,\ bs,\ bg,\ ca,\ zh_CN,\ zh_TW,\ hr,\ cs,\ da,\ nl,\ dz,\ en,\ eo,\ et,\ fi,\ fr,\ gl,\ ka,\ de,\ el,\ gu,\ he,\ hi,\ hu,\ id,\ ga,\ it,\ ja,\ kk,\ km,\ ko,\ ku,\ lv,\ lt,\ mk,\ ml,\ mr,\ ne,\ se_NO,\ nb_NO,\ nn_NO,\ pl,\ pt,\ pt_BR,\ pa,\ ro,\ ru,\ sr,\ sk,\ sl,\ es,\ sv,\ tl,\ ta,\ th,\ tr,\ uk,\ vi,\ cy,\ wo
debconf (developer): --> 0
Mar 26 07:16:40 debconf (filter): <-- SUBST localechooser/languagelist NAMES_EN C, Albanian, Amharic, Arabic, Asturian, Basque, Belarusian, Bengali, Bosnian, Bulgarian, Catalan, Chinese (Simplified), Chinese (Traditional), Croatian, Czech, Danish, Dutch, Dzongkha, English, Esperanto, Estonian, Finnish, French, Galician, Georgian, German, Greek, Gujarati, Hebrew, Hindi, Hungarian, Indonesian, Irish, Italian, Japanese, Kazakh, Khmer, Korean, Kurdish, Latvian, Lithuanian, Macedonian, Malayalam, Marathi, Nepali, Northern Sami, Norwegian Bokmaal, Norwegian Nynorsk, Polish, Portuguese, Portuguese (Brazil), Punjabi (Gurmukhi), Romanian, Russian, Serbian, Slovak, Slovenian, Spanish, Swedish, Tagalog, Tamil, Thai, Turkish, Ukrainian, Vietnamese, Welsh, Wolof
debconf (developer): <-- SUBST localechooser/languagelist NAMES_EN C,\ Albanian,\ Amharic,\ Arabic,\ Asturian,\ Basque,\ Belarusian,\ Bengali,\ Bosnian,\ Bulgarian,\ Catalan,\ Chinese\ (Simplified),\ Chinese\ (Traditional),\ Croatian,\ Czech,\ Danish,\ Dutch,\ Dzongkha,\ English,\ Esperanto,\ Estonian,\ Finnish,\ French,\ Galician,\ Georgian,\ German,\ Greek,\ Gujarati,\ Hebrew,\ Hindi,\ Hungarian,\ Indonesian,\ Irish,\ Italian,\ Japanese,\ Kazakh,\ Khmer,\ Korean,\ Kurdish,\ Latvian,\ Lithuanian,\ Macedonian,\ Malayalam,\ Marathi,\ Nepali,\ Northern\ Sami,\ Norwegian\ Bokmaal,\ Norwegian\ Nynorsk,\ Polish,\ Portuguese,\ Portuguese\ (Brazil),\ Punjabi\ (Gurmukhi),\ Romanian,\ Russian,\ Serbian,\ Slovak,\ Slovenian,\ Spanish,\ Swedish,\ Tagalog,\ Tamil,\ Thai,\ Turkish,\ Ukrainian,\ Vietnamese,\ Welsh,\ Wolof
debconf (developer): --> 0
Mar 26 07:16:40 debconf (filter): <-- SUBST localechooser/languagelist NAMES_BOTH C${!TAB}-${!TAB}No localization, Albanian${!TAB}-${!TAB}Shqip, Amharic${!TAB}-${!TAB}አማርኛ, Arabic${!TAB}-${!TAB}عربي, Asturian${!TAB}-${!TAB}Asturianu, Basque${!TAB}-${!TAB}Euskara, Belarusian${!TAB}-${!TAB}Беларуская, Bengali${!TAB}-${!TAB}বাংলা, Bosnian${!TAB}-${!TAB}Bosanski, Bulgarian${!TAB}-${!TAB}Български, Catalan${!TAB}-${!TAB}Català, Chinese (Simplified)${!TAB}-${!TAB}中文(简体), Chinese (Traditional)${!TAB}-${!TAB}中文(繁體), Croatian${!TAB}-${!TAB}Hrvatski, Czech${!TAB}-${!TAB}Čeština, Danish${!TAB}-${!TAB}Dansk, Dutch${!TAB}-${!TAB}Nederlands, Dzongkha${!TAB}-${!TAB}རྫོང་ཁ།, English${!TAB}-${!TAB}English, Esperanto${!TAB}-${!TAB}Esperanto, Estonian${!TAB}-${!TAB}Eesti, Finnish${!TAB}-${!TAB}Suomi, French${!TAB}-${!TAB}Français, Galician${!TAB}-${!TAB}Galego, Georgian${!TAB}-${!TAB}ქართული, German${!TAB}-${!TAB}Deutsch, Greek${!TAB}-${!TAB}Ελληνικά, Gujarati${!TAB}-${!TAB}ગુજરાતી, Hebrew${!TAB}-${!TAB}עברית, Hindi${!TAB}-${!TAB}हिन्दी , Hungarian${!TAB}-${!TAB}Magyar, Indonesian${!TAB}-${!TAB}Bahasa Indonesia, Irish${!TAB}-${!TAB}Gaeilge, Italian${!TAB}-${!TAB}Italiano, Japanese${!TAB}-${!TAB}日本語, Kazakh${!TAB}-${!TAB}Қазақ, Khmer${!TAB}-${!TAB}ខ្មែរ, Korean${!TAB}-${!TAB}한국어, Kurdish${!TAB}-${!TAB}Kurdî, Latvian${!TAB}-${!TAB}Latviski, Lithuanian${!TAB}-${!TAB}Lietuviškai, Macedonian${!TAB}-${!TAB}Македонски, Malayalam${!TAB}-${!TAB}മലയാളഠ, Marathi${!TAB}-${!TAB}मराठी, Nepali${!TAB}-${!TAB}नेपाली , Northern Sami${!TAB}-${!TAB}Sámegillii, Norwegian Bokmaal${!TAB}-${!TAB}Norsk bokmål, Norwegian Nynorsk${!TAB}-${!TAB}Norsk nynorsk, Polish${!TAB}-${!TAB}Polski, Portuguese${!TAB}-${!TAB}Português, Portuguese (Brazil)${!TAB}-${!TAB}Português do Brasil, Punjabi (Gurmukhi)${!TAB}-${!TAB}ਪੰਜਾਬੀ, Romanian${!TAB}-${!TAB}Română, Russian${!TAB}-${!TAB}Русский, Serbian${!TAB}-${!TAB}Српски, Slovak${!TAB}-${!TAB}Slovenčina, Slovenian${!TAB}-${!TAB}Slovenščina, Spanish${!TAB}-${!TAB}Español, Swedish${!TAB}-${!TAB}Svenska, Tagalog${!TAB}-${!TAB}Tagalog, Tamil${!TAB}-${!TAB}தமிழ், Thai${!TAB}-${!TAB}ภาษาไทย, Turkish${!TAB}-${!TAB}Türkçe, Ukrainian${!TAB}-${!TAB}Українська, Vietnamese${!TAB}-${!TAB}Tiếng Việt, Welsh${!TAB}-${!TAB}Cymraeg, Wolof${!TAB}-${!TAB}Wolof
debconf (developer): <-- SUBST localechooser/languagelist NAMES_BOTH C${!TAB}-${!TAB}No\ localization,\ Albanian${!TAB}-${!TAB}Shqip,\ Amharic${!TAB}-${!TAB}አማርኛ,\ Arabic${!TAB}-${!TAB}عربي,\ Asturian${!TAB}-${!TAB}Asturianu,\ Basque${!TAB}-${!TAB}Euskara,\ Belarusian${!TAB}-${!TAB}Беларуская,\ Bengali${!TAB}-${!TAB}বাংলা,\ Bosnian${!TAB}-${!TAB}Bosanski,\ Bulgarian${!TAB}-${!TAB}Български,\ Catalan${!TAB}-${!TAB}Català,\ Chinese\ (Simplified)${!TAB}-${!TAB}中文(简体),\ Chinese\ (Traditional)${!TAB}-${!TAB}中文(繁體),\ Croatian${!TAB}-${!TAB}Hrvatski,\ Czech${!TAB}-${!TAB}Čeština,\ Danish${!TAB}-${!TAB}Dansk,\ Dutch${!TAB}-${!TAB}Nederlands,\ Dzongkha${!TAB}-${!TAB}རྫོང་ཁ།,\ English${!TAB}-${!TAB}English,\ Esperanto${!TAB}-${!TAB}Esperanto,\ Estonian${!TAB}-${!TAB}Eesti,\ Finnish${!TAB}-${!TAB}Suomi,\ French${!TAB}-${!TAB}Français,\ Galician${!TAB}-${!TAB}Galego,\ Georgian${!TAB}-${!TAB}ქართული,\ German${!TAB}-${!TAB}Deutsch,\ Greek${!TAB}-${!TAB}Ελληνικά,\ Gujarati${!TAB}-${!TAB}ગુજરાતી,\ Hebrew${!TAB}-${!TAB}עברית,\ Hindi${!TAB}-${!TAB}हिन्दी\ ,\ Hungarian${!TAB}-${!TAB}Magyar,\ Indonesian${!TAB}-${!TAB}Bahasa\ Indonesia,\ Irish${!TAB}-${!TAB}Gaeilge,\ Italian${!TAB}-${!TAB}Italiano,\ Japanese${!TAB}-${!TAB}日本語,\ Kazakh${!TAB}-${!TAB}Қазақ,\ Khmer${!TAB}-${!TAB}ខ្មែរ,\ Korean${!TAB}-${!TAB}한국어,\ Kurdish${!TAB}-${!TAB}Kurdî,\ Latvian${!TAB}-${!TAB}Latviski,\ Lithuanian${!TAB}-${!TAB}Lietuviškai,\ Macedonian${!TAB}-${!TAB}Македонски,\ Malayalam${!TAB}-${!TAB}മലയാളഠ,\ Marathi${!TAB}-${!TAB}मराठी,\ Nepali${!TAB}-${!TAB}नेपाली\ ,\ Northern\ Sami${!TAB}-${!TAB}Sámegillii,\ Norwegian\ Bokmaal${!TAB}-${!TAB}Norsk\ bokmål,\ Norwegian\ Nynorsk${!TAB}-${!TAB}Norsk\ nynorsk,\ Polish${!TAB}-${!TAB}Polski,\ Portuguese${!TAB}-${!TAB}Português,\ Portuguese\ (Brazil)${!TAB}-${!TAB}Português\ do\ Brasil,\ Punjabi\ (Gurmukhi)${!TAB}-${!TAB}ਪੰਜਾਬੀ,\ Romanian${!TAB}-${!TAB}Română,\ Russian${!TAB}-${!TAB}Русский,\ Serbian${!TAB}-${!TAB}Српски,\ Slovak${!TAB}-${!TAB}Slovenčina,\ Slovenian${!TAB}-${!TAB}Slovenščina,\ Spanish${!TAB}-${!TAB}Español,\ Swedish${!TAB}-${!TAB}Svenska,\ Tagalog${!TAB}-${!TAB}Tagalog,\ Tamil${!TAB}-${!TAB}தமிழ்,\ Thai${!TAB}-${!TAB}ภาษาไทย,\ Turkish${!TAB}-${!TAB}Türkçe,\ Ukrainian${!TAB}-${!TAB}Українська,\ Vietnamese${!TAB}-${!TAB}Tiếng\ Việt,\ Welsh${!TAB}-${!TAB}Cymraeg,\ Wolof${!TAB}-${!TAB}Wolof
debconf (developer): --> 0
Mar 26 07:16:40 debconf (filter): <-- GET debian-installer/locale
debconf (developer): <-- GET debian-installer/locale
debconf (developer): --> 1 
Mar 26 07:16:40 debconf (filter): <-- GET debian-installer/language
debconf (developer): <-- GET debian-installer/language
debconf (developer): --> 1 
Mar 26 07:16:40 debconf (filter): <-- SET debconf/language en
debconf (developer): <-- SET debconf/language en
debconf (developer): --> 0 value set
Mar 26 07:16:40 debconf (filter): <-- CAPB backup align
debconf (developer): <-- CAPB backup align escape
debconf (developer): --> 0 multiselect escape 
Mar 26 07:16:40 debconf (filter): <-- INPUT critical localechooser/languagelist
Mar 26 07:16:40 debconf (filter): widget found for localechooser/languagelist
debconf (developer): <-- GET localechooser/languagelist
debconf (developer): --> 1 en
debconf (developer): <-- GET localechooser/languagelist
debconf (developer): --> 1 en
debconf (developer): <-- METAGET localechooser/languagelist choices-c
debconf (developer): --> 1 C, sq, am, ar, ast, eu, be, bn, bs, bg, ca, zh_CN, zh_TW, hr, cs, da, nl, dz, en, eo, et, fi, fr, gl, ka, de, el, gu, he, hi, hu, id, ga, it, ja, kk, km, ko, ku, lv, lt, mk, ml, mr, ne, se_NO, nb_NO, nn_NO, pl, pt, pt_BR, pa, ro, ru, sr, sk, sl, es, sv, tl, ta, th, tr, uk, vi, cy, wo
debconf (developer): <-- GET ubiquity/only-show-installable-languages
debconf (developer): --> 1 false