I did some more digging;
So IE doesn't fire a "change" event when you click on a checkbox, it fires the change event when you tab
off the checkbox. Visually the item changed, but until you "accept" the field the change isn't registered.
this is the same as say a text field where you can start typing, and "see" the changes, but the change isn't sent
to the server until it's finished. One of those cases though where the behaviour, while completely consistent, is
completely confusing (and wrong).
BTW You're apparently not the first one to notice this;
http://norman.walsh.name/2009/03/24/jQueryIEI've coded a fix into the JavaScript, which will be in the next build.
Cheers
Bruce