C# - After Disabling A Submit Button With JS, Re-enable After File Download?

I'm working on an ASP.NET application. Currently when the user clicks "Save" on an item, we disable the Save button, change its text to "Saving..." and so on. This works fine, because the button causes a postback which results in a new page being loaded, on which the Save button is no longer disabled.

We now want to apply this to other actions: Publish (not much different from Save), Import (again, much like Save, but based on data the user has uploaded in a previous step), Export (downloads an XML file to the user) etc.

Export is causing me problems - the button stays disabled. I think this is because the server sends back an XML file rather than a new web page, and so the browser just displays the same page.

The server-side code is along the lines of

Response.Clear();
Response.BufferOutput = true;
Response.ContentType = "text/xml";
Response.AppendHeader("Content-Disposition", "attachment; filename=" + whatever);
[push file contents into Response.OutputStream]
Response.End();

a way of making the server send a fresh page back in the response as well as the XML, thus re-enablnig the button in the same manner that the other pages do, ora way of getting the browser/JS to re-enable the button once the file has been sent.