jQuery 1.5 (and 1.5.1rc) and event.isDefaultPrevented in Firefox

jQuery 1.5 (and 1.5.1rc) and event.isDefaultPrevented in Firefox

I'd like to draw attention to this post from the using jQuery forum as I've run into the same problem. It seems that in jQuery 1.5 (and 1.5.1rc) event.isDefaultPrevented is set to true in Firefox regardless of whether the event has had its default prevented:

http://forum.jquery.com/topic/jquery1-5-isdefaultprevented-always-return-true-in-firefox-for-some-events

Is this expected behaviour? If so is there a workaround?