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 <defunct> 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 <defunct> 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?