ajaxToolKit:ModalPopupExtender keep open after postback

i have an ajaxToolKit:ModalPopupExtender that has an update panel with a fileupload control - it works fine with a postback trigger 

however, after i upload the file, the ajaxToolKit:ModalPopupExtender hides - how do i keep it showing after the postaback and after i upload the file?

thanks for your help