As I said earlier, we didn’t test our solution to using the ModalPopupExtender in SharePoint in all situations. Today we made a start to do so. To indicate our successrate: we now use window.showModalDialogwith some extra pages…
Lets go through some of the problems we encountered.
Placing an UpdatePanel around the entire UserControl (with default settings) makes that the entire UserControl is posted back, even when it is a control inside a nested UpdatePanel that posts back.