This is just a tiny update that has a small workaround for the Fullscreen Alt Tab issue.
There is now a new resolution option called AUTO that will auto set the screen size to the desktop resolution and make it borderless windowed. This new system allows for alt tabbing or anything else that breaks the focus of the game.
As an unfortunate side effect  the program will now need to be restarted in order for changes to take effect.
I have currently left the old fullscreen options in and the old rules still apply to them. I will probably remove the old fullscreen functions in the future and tidy up the graphics menus to look a little tidier and less confusing.
But for now go to Options>Resolution>AUTO>then restart Dungeons of mysteria in all its fullscreen Alt tabable glory...