System assumes DualScreen setup

[Czechnology]

After one Windows Update, Windows always assumes (after turning on or docking in etc) that I have two displays running, so I have to manually turn that off every time.
Is there some way I could tell it to keep it single-display?

The proable problem-related update: ATI Technologies Inc. - Display - ATI Mobility Radeon HD 3400 Series

(in the beginning it even caused big problems as it assumed laptop's display was secondary and was showing no login screen (only mouse, if it got in the secondary display) and after logging-in only the wallpaper)

Thanks in advance