The F5 key was used open the Save-dialog in SCUMM games. The SVN-version of ScummVM supports these dialogs by pressing Alt-F5. This does not work with the FM-Town versions of Zak and Indy3. For these games the most significant bit of _mouseAndKeyboardStat has to be set if a special key like F5 (keycode 0x8005) or joystick buttons (keycode mask 0xFE00, e.g. SELECT=0xFE40 for the save/load menu) is pressed.
Hence the distinction with (_mouseAndKeyboardStat < MBS_MAX_KEY) between mouse- and key-events is not applicable with FM-Towns games.
The patch is a little workaround that remaps the F5 key.
Ticket imported from: #1687010. Ticket imported from: patches/726.
Makes perfect sense -- and a nicely written & documented patch, thanks a lot :).