[KHS]

Did the app get suspended and restarted by windows? If so, that would do it, as the checkmark state isn't saved in the suspended state. You can avoid this by running the app in windowed mode instead of in full screen mode (hit F11 to exit fullscreen mode). In Windowed mode, Windows won't suspend MobileSheets so you can alt-tab without any issues. I'm sorry you lost all that time though.

Mike

But it's a Windows application, not a Microsoft Store "app" and I ought to be able to Alt-Tab to and from it in ANY window state, perhaps the only exception being if I've deliberately put myself into "Performance" mode where I don't want anything, including my own errant keystrokes or mouse clicks, to interrupt my use of MSP. Does Microsoft require that your application be "suspended and restarted" just because I'm running it full screen? If so, can you warn the Alt-Tab'er that he's about to wipe out all his work unless he first enters windowed mode? Is there anything important OTHER than checkmark state that I must make myself aware will be discarded if I ever Alt-Tab out again while in full-screen mode?