Hi, not a bug.
Is that Windows 7? I see your enhanced Windows rendering engine is disabled (do you have hardware acceleration?). Try reenabling it and that will be gone.
What happens is that, with less memory assigned to video memory, QB64 windows (which are OpenGL surfaces) won't be updated unless _DISPLAY is called again. In your case, the IDE is hung waiting for your program to end, and because of that it is not updating the OpenGL surface buffer.
Either turn on Windows's advanced rendering engine again (usually by setting the desktop theme to Windows 7's default with the glass effects) or, instead of hitting F5 to run your program, hit Ctrl+F5, which will run it detached from the IDE.
PS: The "Bugs" thread is closed because the Admin will only move there topics that are really bugs, which is why this type of inquiry should really be posted here, in Discussion. (notice the board's description: "Topics in QB64-related deemed bug-related are moved here by admin.")