Turn off the "Use Graphic Processor" option in the Performance section of Preferences. That should clear this up.
99jon: This is a workaround, sure - but I'm used to use the keyboard for navigation and I would be much more happy to solve the problem instead of avoiding any cursor key actions. Even when I wrote it happens in library, a longer cursor key press in development section brings me far away from my processed picture.
Just Shoot Me: Already tried that, it might be a little(!) better but far away from good.
I probably wouldn't complain when LR4 didn't work really good w/o these problems.
Additional information: I use a notebook, i5 6GB Ram, SSD (normal HD makes no difference, tried), Win7
However: Thanks for your responses
At the moment, I use a workaround: OS settings of keyboard repeat are now set to "long delay" and "slow repeat". That is still far away from good but at least better.
I still hope for a better solution (or a patch by Adobe)