When the wavenc stops, it seeks to the beginning of the file to update the
headers using 

  event = gst_event_new_seek (GST_FORMAT_BYTES | GST_SEEK_METHOD_SET, 0);
  gst_pad_send_event (GST_PAD_PEER (wavenc->srcpad), event);


It don't know why but this doesn't seek to the beginning.  It can be fixed by
using  
  event = gst_event_new_seek (GST_FORMAT_BYTES | GST_SEEK_METHOD_SET, 0);
  gst_pad_push(wavenc->srcpad, GST_DATA(event));

I'm not sure if the bug is in gst_pad_send_event() or wavparse.