I've used ZD for awhile now, and all of a sudden yesterday, something funky has happened with the GUI.
Basically, the window is somehow "locked" in maximized position on my left monitor and there is no title bar and thus no min/max/etc buttons. Keyboard shortcuts for restore or move don't work. It will minimize with key shortcut (disappear) but that's all.
Upon open, it opens as usual in a small window, then near the end, suddenly snaps to the position I described. All mail functions seem to work normally, just a GUI thing.