Binary package hint: ubiquity
Image is lucid-desktop (armel+babbage & i386) Alpha 2 Release.
To reproduce this, select next until step 3. Set the correct location and click next. Click back, and before the program goes to check internet time, click quit. Ubiquity will lock in an endless loop. Quit confirmation dialog can be moved around and the screen will redraw. Eventually, the whole system hangs (although that may be another issue).
/var/log/syslog from live image attached, but nothing relevant in there. /var/log/partman doesn't exist as that step was never achieved.