Comment 5 for bug 278471

Same here, login screen doesn't flicker, neither does Gnome session.

05:00.0 VGA compatible controller: ATI Technologies Inc Radeon HD 3850

Different display adapters and drivers - probably a Xorg or KDE4 bug. I'm betting KDE4 - Xorg doesn't seem to have been updated for a while and this just began occurring yesterday. I've been using Intrepid for several weeks now, running aptitude dist-upgrade daily.