valve and mp4mux break a pipeline flow

[Grégoire Gentil]

I have the following video pipeline:

filesrc ! qtdemux name=demux ! queue ! h264parse ! valve drop=false ! 
mp4mux name=mux ! filesink

If I turn true/false the drop property of the valve element, the 
pipeline continues running and the video input "advances" as it should 
be. So far, so good.


If I add audio with a fakesink to the pipeline:

filesrc ! qtdemux name=demux ! queue ! h264parse ! valve drop=false ! 
mp4mux name=mux ! filesink demux. ! aacparse ! valve drop=false ! fakesink

everything works fine the same way as above.


But if I link audio to mp4mux:

filesrc ! qtdemux name=demux ! queue ! h264parse ! valve drop=false ! 
mp4mux name=mux ! filesink demux. ! aacparse ! valve drop=false ! mux.

when I turn true both valves at the same time, the pipeline gets stuck. 
The buffers are not flowing anymore.


Any idea why and how I could fix this problem?

Grégoire