I can't reproduce this. I'm using the following:
$ emacs -fn 'Ubuntu Mono 20' C-x 8 enter 2227 enter C-x 8 enter 2228 enter
$ emacs -fn 'DejaVu Sans Mono 20' C-x 8 enter 2227 enter C-x 8 enter 2228 enter
Florian, could you possibly post the exact sequence of instructions that you're using when you're seeing this?
I can't reproduce this. I'm using the following:
$ emacs -fn 'Ubuntu Mono 20'
C-x 8 enter 2227 enter
C-x 8 enter 2228 enter
$ emacs -fn 'DejaVu Sans Mono 20'
C-x 8 enter 2227 enter
C-x 8 enter 2228 enter
Florian, could you possibly post the exact sequence of instructions that you're using when you're seeing this?