This should be a quick "yes" answer - I am in the process of creating a very simple test, but I thought I'd ask on here too (also, so other people might be able to find the answer, if they have the same problem).
I have created a modalpopupextender that opens up a panel containing an update panel. I have a cancel button that is tied into the MPE's [CancelControlID] property and this closes the popup when I click it. However, if I perform a partial postback within the update panel, the cancel button no longer works. I have found an example online that seems to imply that the cancel button (and I'm guessing, by association) and the OK button should be outside the update panel. Does the partial postback break the buttons' client script bindings, and thus should they always be placed outside the update panel?