timerId has to be set to true, to avoid starting multiple animation queues

src/effects.js

@@ -363,9 +363,9 @@ jQuery.fx.prototype = {
 		t.elem = this.elem;
 
 		if ( t() && jQuery.timers.push(t) && !timerId ) {
-			jQuery.support.requestAnimationFrame ?
-				window[jQuery.support.requestAnimationFrame](fx.tick):
-				timerId = setInterval(fx.tick, fx.interval);
+			timerId = jQuery.support.requestAnimationFrame ?
+				!window[jQuery.support.requestAnimationFrame](fx.tick):
+				setInterval(fx.tick, fx.interval);
 		}
 	},