It seems like the target and relatedTarget properties of the synthetic "mouseenter" event are reversed. (The target should be—but isn't—the element being entered.) I'm not familiar enough with the code to know how it's supposed to work, but it seems like the wrapped native event is a "mouseout" event and the properties are never being swapped to account for that fact.

Here's a reduced test case:
http://jsfiddle.net/matthewwithanm/sVmer/