I'm no expert on this, but based on what I remember it is possible that (depending on the file size) the video gets buffered in the browser in less than 30s. Their servers might deliberately break the connection (by sending TCP RST) if it lasts longer, to prevent this kind of streaming.
I've also seen this with some of shunte's plugins (wdviacomm).
To debug this, you would need to do a packet capture on the wdtv (using tcpdump for instance) and see how the session is broken. If the server sends RST, then the media player is not required to re-attempt to reconnect (as stated in the RFC).
If the transfer lasts longer, you should check if there is an alternate communication going on - something like a keep-alive -where the browser sends some requests every 30s. If the requests don't make it to the server in time, then it will cut the connection. I've seen something like this in noname's plugins (wdflix or noname, I don't remember which one).