It was also funny, that after starting "camstudio" the glitches ended. But that's the only software, I know.
I think it has something to do that the software disables the resizing of different windows.
The problem also disappears, when I use the taskbar over the whole lengh of the 3 monitors. Nvidia luckily presents an option, that only shows the bar on the middle screen. Something, that Start8 can't really handle so far.