I couldn't find a place to file bugs, so I'll try here...
I just installed FreeFileSync 6.5 on Windows 7, and when I maxmimize its window, the window doesn't match the screen. It is about 16 pixels too far down, i.e. 16 pixels from the screen's top border. It also seems to go about the same amount under the Windows task bar in the bottom.
Oh, I restarted FreeFileSync, and now it does not happen anymore!