When pressing M the spell casting window comes up and pressing ESC dismisses it.

Pressing M more than once, however, causes multiple stacked versions of the window which require hitting ESC the same number of times to dismiss.

To Reproduce:

1) Hit M to bring up spell window

2) Hit M twice more

3) Press ESC once, notice that spell window is still there

4) Press ESC twice more to dismiss overlapped windows

The correct behaviour for pressing M again after the spell window is already up is to dismiss the window.  This is standard behaviour on virtually ALL games.  ie Press M once to bring up window, press either ESC or M again to dismiss.