I am very sorry for posting too quickly.
The problem indeed doesn't have to do with Fences. Same happens on another computer with a very fresh Windows 7 installation.
And by Google I found that I'm not alone with this.
I am suspecting my mouse now which has 1000 Hz polling rate... but it's just strange that these peaks don't happen when moving it anywhere else (in a browser, or inside another window on desktop).
Thread can be closed or deleted, thanks.
