Problem:

var e2 = [e1 is a child of e2 but could also be e2];

$(e1).mouseleave(function() {

event.stopPropagation();

isChild = $(e2).find("*").andSelf().is(e1);

if(isChild) alert("This alert is NEVER reached :(");

});

Solution:

replace isChild so that,

isChild = e2.find("*").andSelf().not(e2.find("*").andSelf().not(e1)).is(e1);

It appears that "not()" is the only traversing function working in this case.