Hi Akiono Wan,
Thank you for reporting this. I was able to reproduce this issue. We have made some changes around the UI related code of the RadUpload and this was a side product of this. The state was incorrectly updated when automatic upload was enabled. I have already resolved this and updated your Telerik points accordingly. The resolution will be available with the next internal build.
the Telerik team
Browse the videos here>>
to help you get started with RadControls for Silverlight