I have exactly the same problem with lg-42LB730V. I spend hours to get down to the problem. I think its something to do with transcode... I cant rewind or forward most of the videos streaming from the NAS thought wired LAN connection but I can rewind or fast forward When I copy paste them into a memory stick Or hardrive and stream from the USB. It is annoying but looks like a bug to me... I don't think there is a solution until there is a webos firmware update.