I have a wizard-like screen that has several steps. The first step includes an async-upload. I have set the PostbackTriggers property so that only the submit button on the last step causes the file to be uploaded. This all works fine to persist the file upload through the postbacks associated with the Next/Previous buttons of the wizard, however, the way the wizard works is to hide/show panel controls depending on which step is currently being viewed. If I set the panel.visible property to false for the panel which contains the async-upload, I notice when I return to this step by setting panel.visible to true, the upload is gone. I have found one potential workaround by setting panel.Style("display") = "block" or "none" depending on whether I want to hide it or not and this seems to persist the upload. I would prefer to use the built-in asp.net visible property. I am wondering if this is a known limitation or am I doing something wrong?