TRANSITION_END is dispatched for each transition (show and hide). There is a property on transitionEnd event, transitionType that can help you to do that.
Here is an example:
myEffect.addEventListener(FLASHEFFEvents. TRANSITION_END, transitionEndHandler);
function transitionEndHandler(evtObj:FLASHEFFEvents):void {
if(evtObj.transitionType=="hide"){
trace(transitionEnd)
}
}