On my Windows 7 box with a 768px screen, wm maxsize returns 750. This does not take into account the size of the task bar, which means that natural height of windows can be more than the \"usable\" screen height, making the window appear _behind_ the task bar (see screenshot).
This problem is visible e.g. when one widget has a fixed height, but the one stacked below it does not. In that case, the window\'s natural size should be limited to the usable screen size so that it stops right above the task bar. What happens at the moment is that the second widget, which has no fixed size, only shrinks when the window would exceed the value of \"wm maxsize\". This example (used in the screenshot) illustrates the problem:
toplevel .w
text .w.t1 -height 25
text .w.t2
grid .w.t1
grid .w.t2
update
wm geometry .w
wm maxsize .w
(Just change \"-height 25\" so that the first text box takes the most part of your screen\'s height.)
This problem also happened with Tk 8.5. I have not tested this under Windows 7 SP1 (upgrade bug).
Screenshot illustrating the bug with Wish 8.6