There was another comment about this, it's not what I had thought it was. Looks like the system settings for window frame padding is different depending on the OS. This is one of the problems with MS. I don't have Win8, so I can't test it on that OS. There's a reason I limited the size ( a kludge related to the graphs). I'll see if I can find a way around the issue.
I fiddled around with some settings and found that changing the "Change only the text size" option for title bars from 12 (the default) to 11 fixes the problem. I guess windows has changed that title bar size in win8 & the fixed window size must include the title bar hence it then doesn't have space for the actual content pane.