When I play a clip like this:
ges-launch-1.0 +clip file:///C:/tmp/videos/b.mp4

The clip is 9 seconds long and plays fine. But after it's played, the timeline restarts and the videosink goes completely black for the same amount of time as the clip length. After that the validation is displayed and application stop.

If I add a specific duration to the clip, then the clip is played for the specified time. But, additionally the black screen is also show for the duration time.

If I add and other clip both are played, but there is black video in-between the clips and after the second clip.