Create a 2D window and then manually focus a different window on your desktop, call SDL_PumpEvents() so the X11 driver sets its this->hidden->switch_waiting, then set a fullscreen OpenGL window (which makes the X11 driver tear down and create a new window instead of just resizing the existing one), poll for events, and the newly-created window will think it needs to pop back to a window. Fixed by resetting switch_waiting to zero if X11_CreateWindow() had to tear down a previous window.

#ifndef _SDLname_h_
#define _SDLname_h_

#if defined(__STDC__) || defined(__cplusplus)
#define NeedFunctionPrototypes 1
#endif

#define SDL_NAME(X)	SDL_##X

#endif /* _SDLname_h_ */