Windows 7 auto-adjusting volume control

Whenever i try to increase the volume of my system from the tray icon , the volume control bar goes back to its initial position.This behaviour started after I used the volume mixer. Anybody knows what's happening?

Using Windows 7 64 bit, latest SP's installed.

PS: I made a video capture of what's happening, but can't seem to be able to upload it.

There's a setting which may be causing this. Go to your sound options (right click the systray icon and click playback devices) then click "Communications", select "Do nothing". If something is triggering your communication channel it'll reduce your audio.

Did you check to make sure that none of your keys are stuck? For instance, some laptops allow you to press the Fn Key plus a key in the numeric pad to control volume. If these keys are stuck, then that would cause weird volume control actions.