If you try to change size of Standalone window, then switch to something else and then will give focus back to the window - it will reset it’s size and position to initials.
I believe it’s a bug, because the code, that controlling this annoying behaviour:
// As we've just been activated, attempt to restore the resolution that the engine previously cached. // This allows us to force ourselves back to the correct resolution after alt-tabbing out of a fullscreen // window and then going back in again. Renderer->RestoreSystemResolution(ActivateEvent.GetAffectedWindow());
was supposed to be triggered only for the case of going to full screen mode and back.
Commenting this out solves the issue and does not harm Alt+Enter / Alt+Tab switches.