grub2 shows both theme-styled menu and text-based menu

[Timur Nitt]

This behavior matters Ubuntu 17.10 (since last upgrade on 2018-03-02, 2.02~beta3-4ubuntu7.2) and Ubuntu 18.04.
A theme is set in /default/grub as GRUB_THEME=/boot/grub/themes/poly-light/theme.txt. Before this upgrade the theme-based menu entries were shown normally without overlayed text menu.
The attachment shows the effect: now both kind of menus are shown at the same time and both menus are selectable at the same time. While selecting one of the menu entries both menus are flickering ('fight' to be at the top). It is independent from different themes and screen resolutions.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[EmilioEA (emilio.ea)]

I can confirm the same behavior. With the last update, the grub screen flickers quite a bit.

[Timur Nitt (tnitt)]

There's a workaround to hide the ugly text-based menu: I've checked the /boot/grub/grub.cfg file and find out, if you change the line and its content

  'terminal_output --append gfxterm'

to

  'terminal_output gfxterm'

in paragraph '00_header' the text-based menu won't be shown.

Paragraph '00_header' is part of file '/etc/grub.d/00_header', which is part of package 'grub-common'.

Warning: Editing the line and its ensuing behavior is checked while 'GRUB_THEME' is set to a theme file only.

[Timur Nitt (tnitt)]

You can ignore the last warning I wrote. The edited text works in both cases, if you set 'GRUB_THEME' or not.
For me, I changed

  terminal_output --append ${GRUB_TERMINAL_OUTPUT}

to

  terminal_output ${GRUB_TERMINAL_OUTPUT}

in file '/etc/grub.d/00_header' and exe'ed an 'update-grub' - that's all.

[Ray Timer (raytimer)]

Thumbs up, Timur! Worked great on both of my PCs!

[Phil Veal (pmveal)]

The problem was introduced by LP: #1743884 -

+diff --git a/util/grub.d/00_header.in b/util/grub.d/00_header.in
+index 674a76140..b27d0b17a 100644
+--- a/util/grub.d/00_header.in
++++ b/util/grub.d/00_header.in
+@@ -267,7 +267,7 @@ case x${GRUB_TERMINAL_OUTPUT} in
+ ;;
+ x*)
+ cat << EOF
+-terminal_output ${GRUB_TERMINAL_OUTPUT}
++terminal_output --append ${GRUB_TERMINAL_OUTPUT}
+ EOF
+ ;;
+ esac

I have temporarily downgraded the following packages to 2.02~beta3-4ubuntu7.1 -

$ apt-mark showhold
grub-common
grub-pc
grub-pc-bin
grub2-common