Switch windowed mode / fullscreen mode Resolution

switch windowed mode / fullscreen mode UMG buttons and mouse position will no longer match up.
This makes it very difficult to interact with UMG elements

It seems as though the new view-port size/Resolution is not being updated in Slate/UMG, and is using the old size to calculate the mouse location, which is incorrect.

You have to save this information in the save game file. And then read that when the game restarts, and set the window mode.