Comment 2 for bug 1899190

Thank you for the bug report.
This situation heavily depends on the Window Manager: some will allow a window to pop in front of a fullscreen window, and some won't.
However, in case of a game, it is annoying enough that it truly deserves a patch; therefore I made one that should prevent the problem (commit 7df0709e1f50652d5204492fd7372ef794e92279).