Flip() bug

Framework brl.GLGraphics
Import brl.standardio

Graphics(800,600,32)

While Not KeyHit(KEY_ESCAPE)
	If KeyHit(KEY_F1) Flip 1
	glClear COLOR_BUFFER_BIT
	GLDrawText "FPS: "+FPS(),0,0
	GLDrawText "1. Alt-Tab to Desktop",0,15
	GLDrawText "2. Alt-Tab back to this app",0,30
	GLDrawText "3. Notice that FPS has fallen to 60",0,45
	GLDrawText "4. Press F1 to fix FPS bug",0,60	
	Flip(0)
Wend

Function FPS#()
	Global last:Int
	Local time:Int
	time=MilliSecs()
	Local elapsed:Float=time-last
	last=time
	elapsed=Max(elapsed,1)
	Return 1.0/elapsed*1000.0
EndFunction

	static int _sync=-1;

	if( !_currentContext ) return;
	
	sync=sync ? 1 : 0;
	if( sync!=_sync ){
		_sync=sync;
		_setSwapInterval( _sync );
	}

	SwapBuffers( _currentContext->hdc );