ModalPopupExtender OK and Cancel buttons do not work after update panel postback

[MV]

I have an ModalPopupExtender with a ajax update panel inside. the ok and cancel buttons work fine innitially. but once a partial postback is caused, they stop working.I've found other people have encoutered this problem but did not get a sutible answer. (one such unhelpfull answer is to hide the popup in code behind - an extra round trip I'm trying to avoid.)thanks in advance,mamashare