PTCViewer in ASP.NET

I am trying to use the PTCViewer control in an asp.net page, but am running into a persistent problem. The page loads fine, and the control renders the image correctly -- but when I close the page, it seems to "hang" the browser until I manually end the task. There is nothing else going on with the page (no load/unload events, no other controls, etc.). It happens every time with both IE6 and IE7. Any suggestions would be greatly appreciated. Thanks.