That's a 2 year bug (as I can see from previous reports last good working version was 3.54 - 8/7/14 ) .
Case 1:
Took a 1080p mp4 video from youtube .
- Make a Clip A with let say time 00:20 - 00:30 .
- Copy / paste it to Clip B & C .
- Reversed Clip B
-> Preview cache never finished (cpu 100% always with no progress over 10 min) .
-> Deleting Clip A from timeline, deletes B & C. No clip exists in timeline but theres a clip existing in storyboard !.
The case Repeated to another PC , same result .
I thought that something was going wrong with the specific file . So I made another test.
Case2:
Took a 720p video from Samsung smartphone
- Make a Clip A with let say time 00:20 - 00:30 .
- Copy / paste it to Clip B & C .
- Reversed Clip B
-> Took ages to finish preview (compared with other software).
-> Clip B lost (again) start and end points .
.
Same cases worked great with a 3.51 . Took some seconds to preview the reverse video .
Am I the only guy reversing videos ? 
(Jee don't tell me the trick with another sequence ... )