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.

Makefile.in
Makefile
.libs
*.o
*.lo
*.la
SDL_systhread.c
SDL_systhread_c.h
SDL_syssem.c
SDL_syssem_c.h
SDL_sysmutex.c
SDL_sysmutex_c.h
SDL_syscond.c
SDL_syscond_c.h
clone.S