I see this bug, too. It happens every time I save _the last unsaved_ image with less than 65536 colors (i.e., when no other unsaved files left!). The file is saved correctly. The program doesn't seem to hang, the semi-transpatent tool windows continue to react when I hover the mouse over them, though no controls react to interaction. If I use the task manager to close the program, it is closed instantly as if I would close it normally (as no unsaved files left). Seems like it tries to show a modal dialog box but forgets to bring it to front (and it's hidden behind the main program window). A say so because if you open a "Save as" dialog and try to interact with the main window you will get the same result except that the "Save as" dialog may be navigated with the Tab key and closed with the Esc key.