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.

#include "Processes.r"

resource 'SIZE' (-1) {
	reserved,
	acceptSuspendResumeEvents,
	reserved,
	canBackground,
	doesActivateOnFGSwitch,
	backgroundAndForeground,
	getFrontClicks,
	ignoreAppDiedEvents,
	is32BitCompatible,
	isHighLevelEventAware,
	onlyLocalHLEvents,
	notStationeryAware,
	useTextEditServices,
	reserved,
	reserved,
	reserved,
	5242880,		// 5 megs minimum
	5242880			// 5 megs maximum
};