If I mux a matroska file using the following (note it's matroska with streamable=1 and h264 with b-frames):

gst-launch-1.0 videotestsrc is-live=1 ! \
     video/x-raw,width=1280,height=720,framerate=24/1 ! \
     timeoverlay !     x264enc bitrate=4000 ! \
     video/x-h264,profile=main ! \
     queue ! \
     mux. audiotestsrc is-live=1 wave=0 ! \
     audio/x-raw,channels=2 ! \
     faac ! \
     queue ! \
     mux. matroskamux name=mux streamable=true ! \
     queue ! \
     filesink location=test.mkv

And later demux it with:

gst-launch-1.0 filesrc location=test.mks ! matroskademux name=demux ! h264parse ! fakesink

Only PTS is set, and the DTS is lost. This may result in choppy playback, or confuse other muxer when transmuxing.