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.

#!/usr/bin/perl
#
# Program to take a set of header files and generate DLL export definitions

while ( ($file = shift(@ARGV)) ) {
	if ( ! defined(open(FILE, $file)) ) {
		warn "Couldn't open $file: $!\n";
		next;
	}
	$printed_header = 0;
	$file =~ s,.*/,,;
	while (<FILE>) {
		if ( / DECLSPEC.*SDLCALL ([^\s\(]+)/ ) {
			print "\t$1\n";
		}
	}
	close(FILE);
}
# Special exports not in the header files
print "\tSDL_RegisterApp\n";
print "\tSDL_SetModuleHandle\n";