The fix implemented for #3533 caused a regression in jQuery 1.4.1 (and remains in 1.5). JavaScript exceptions thrown within a plain JS object's on<event> handler get caught and swallowed by event.js:378.

#!js
var Test = function() {
    this.onclick = function(e) {
        throw new Error('This exception will be swallowed.');
    }
};
var obj = new Test();
$(obj).click();

Full test case here. Note that changing jQuery back to 1.3.2 yields the expected behavior.

The exception is swallowed because the fix for #3533 was to wrap the call to on<event> handlers in a try/empty catch. I've created a patch which instead checks if the element being triggered is a <table> and if so, skip calling the on<event> function if the event type contains a colon.

My double-checking of the IE bug corrected by #3533 shows that <table> is the only element that triggers the bug.