Some additional even more strange information about this bug.
Immediately after Gnome start I saw following X-related processes:
2920 tty7 00:00:04 Xorg
6324 tty1 00:00:00 Xorg
6306 tty1 00:00:00 startx
6323 tty1 00:00:00 xinit
But after several minutes the situation has changed:
2920 tty7 00:00:45 Xorg
6481 tty1 00:00:00 xinit
6498 tty1 00:00:00 xinit
6464 tty1 00:00:00 startx
I think something causes start X again on tty1 but I can't figure
which script do this and how. There is no such problem on none-live
wheezy installation, so likely it is something in live start scripts.
Does anyone have any ideas what is it?