Invalid effect when passed to toggle method throws an exception only the first time its called

Invalid effect when passed to toggle method throws an exception only the first time its called

In code below, I am using toggle method from jquery ui library to animate a div.
The first parameter is the name of the effect like fold or drop or bouce.

When I pass an invalid effect like `xyz` then the code below throws an exception that gets caught by the catch block.
However, on subsequent re-runs of the same code no exception gets  thrown and also no animation happens since `xyz` is not a valid effect.

Question : Why the error for invalid effect is only being thrown when this code runs the first time, but not on any runs after that?
I have a demo of this problem at this jsfiddle url:  http://jsfiddle.net/sun21170/rm580npe/7/
  1. var emt = $("#cDiv"); try { emt.hide(); emt.toggle("xyz", { easing: "swing" }, 1000, function() { animationCompleted = true; startPolling(); }); } catch (e) { console.log(e.message); }