Stepping backwards then forwards 1 frame completely breaks webm playback
Using the shortcuts ',' and '.' to step single frames breaks the playback of webm videos. The video becomes un-resumable, the progress bar displays incorrectly, etc. You can reproduce this easily by opening a webm file and going forwards and backwards a few times using those shortcuts. The debug output spits out the error: GStreamer-CRITICAL **: 11:14:16.929: gst_segment_do_seek: assertion 'start <= stop' failed