Where do they appear?  What kind of random characters (english??) Do you have a 
floppy in the drive (though I can't reproduce it with it in or out.)

The effect seems to happen only the first time a user starts gmc (e.g. create a
user (as root), login as this user and try to eject a media).

The chars appear in the window where e.g. '/bin/mount: ...' will be shown
normally and they are in the full 8bit range. It doesn't matter if a floppy is
in the drive or not -- it happens in both cases, but with different "messages".

Still in beta2; will append a screenshot

Created attachment 8089 [details]
Screenshot

deprecated for nautilus