unfiled → event
Thanks for taking the time to contribute to the jQuery project by writing a bug report and providing a test case! After checking your report and test case it's unclear why you did report this for version 1.3.1? Anyhow, this isn't a jQuery issue but a browser issue. From focs() documentation.
This event is implicitly applicable to a limited set of elements
The focus is used to determine which element is the first to receive keyboard-related events.
In recent browser versions, the event can be extended to include all element types by explicitly setting the element's tabindex property
Also look at e.g. quirksmode focus table (may not be uptodate) which gives a nice impression on how differently this event is supported across browsers.
In Chrome/Safari certain elements simply don't get the "keyboard focus" when clicking on them, you can see that they are not highlighted and that e.g. hitting ENTER/SPACE doesn't do anything to the e.g button you just clicked. But you can give these elements the focus by using the TAB key and voilà the event is triggered.
This is actually a Webkit bug (bug #22261) and it isn't clear if they are ever going to fix this or just keeping it like this because that's how Mac/Safari did this the last 8 years.
test case where you can try out the TAB focus thingy and see that tabIndex makes also the stuff in the 3rd box focusable.
I guess this is a wontfix but leaving it still open so others can share their view on this one.