Level Sequence with Media track hangs when scrubbing the timeline

Adding a media track(.mp4/avi) into a level sequence causes the editor to hang when scrubbing the timeline, or enabling/disabling the media track.

1. Create a Sequence and add a camera to it.
2. Key some random movements to the camera track
3. Add a media track and assign a file (.mp4/.avi) media to it
4. scrub the track or enable/disable the media track 

Expected 
Level Sequence Editor scrubs and functions normally

Result
Editor Hangs