All right, I've narrowed the problem down to the new text2screen. When text2screen from the 1.x version of initrd-progs is used, the problem happens. If the stock version of text2screen is used, there is no problem.

So backupmenu does the chroot and after that, the new t2s doesn't react in the same manner as the old one. Is it expecting a file to be there that isn't copied by BackupMenuLauncher.item?

...thinking...