Eric, Sandro is talking about the fact that if you use the platform/browser specific method to deselect the *last* keyword that is selected, and then you click submit...nothing happens.  That is, that keyword is still set.  To unset it, you have to actively select '- no selection -' and hit submit, which is not particularly intuitive.  Presumably the server side code is doing nothing in the case where "nothing is selected", instead of unsetting the last flag.  This should in theory be fixable :)