I have this problem too and after some investigation, I found that on my system doing a soft reboot (windows restart, not a power down) then starting Cubase sorts it out temporarily. IMHO this would seem to indicate Windows 8 install is either screwed up or more likely has some kind of instability in it’s UI code. Steinberg could be struggling with that.
It’s odd that a hard reboot of Windows 8 brings the problem back again but there it is.