Thank you for reporting this issue.
We confirm the issue with dragging the slider's thumb beyond the stream-progress boundary. We will address it as soon as possible and we will inform you in this thread. Please keep an eye on this thread for further information.
About the "video should update as the progress bar is changing":
The current development state of the RadMediaPlayer conforms to this scenario. Attached you can find an example application and drag the slider's thumb to test it (please wait until enough part of the video data is downloaded in order to avoid the lock-issue).
the Telerik team
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