I have similiary the same problem.
In my page i have a grid with manual update and delete comands that go to the server and do their proper things.
The problem is, every time i go to the server and back (without using the radAsyncUpload) the RadAsyncUpload gets hidden/cleared.
I have set the PostBackTriggers to a button in my page that deals with the reading of the files. But it doesn't solve.
At this time i am not looking to preserve the files (cause im not even using the RadAsyncUpload).
I just want to preserve the RadAsyncUpload itself.
Adding another information. After this happend i go to see the source code of the page, and the input of the RadAsyncUpload is type="hidden".
Can anyone help me?