[mythtv] extremely slow switching of live preview with multiple backends

[cmisip]

If I have live preview on one system, when I go up or down the watch
recording screen, the system appears to "hang" but after 5 or so
minutes, it displays the live preview of the current selected video
recorded on another backend.  I thought it was crashing but it turns out
I just wasn't waiting for it to finnish.  This has got to be a bug.   
Thanks.