Hi - I've been hitting a strange bug where callbacks are not invoked when a JSON response is returned from an AJAX call under jQuery 1.4.1.  I just upgraded my app; this was working perfectly pre-1.4.

I do specify the return type as "json" when I invoke $.post . When a simple JSON string like "false" is returned, the callback is invoked. It seems to fail with more complex types, specifically with JSON objects, i.e., {"a":1, "b":5} .

If it helps, I'm running Firefox 3.5 on Ubuntu. In my test environment, the only installed extension is Firebug.