Running Windows Vista 64-bit with SP1, I have found that Klok 1.5 beta (downloaded tonight) forgets the position of the view tabs in the weekly view. So if I set it to show from 10:00am to 6:00pm, the next time it starts, it shows 0:00 to 6:00am. I didn’t have this problem on XP SP 3.
The logic for remembering the current viewable window had some issues in that it tried to show the current time rather than the window you last used. In version 2 (download the beta at http://klok.mcgraphix.com/klok/betaProgram.htm) that has been resolved.