I also use v6.30 with D7 and I am experiencing a similar problem.
After I maximize, minimize, restore, maximize (a few times), minimize button doesn't work (happens when the window is maximized). Actually it looks as if it doesn't detect the mouse release and button is displayed pressed. At the 3rd click (and release) minimize button works.
Edit: Happens when both AllowGlowing and ExtendedBorders are set to true.
just now i had the same problem window was maximized i pressed minimize and the whole window content disappeared but the caption was there and the whole window looks as if it has 1 blank panel. restoring and minimizing again: the window was shown and didnt minimize clicking minimize the 3rd time: made it minimize ok