The reason I am stressing that point is because your coworker Q missed that note, and mistakenly suggested that he fixed the problem without Restarting the Editor. Then he abruptly left the conversation. 
Here is that report with the same bug triggered from 2 Sequence references. In that case the problem is even worse, because the references cannot even be removed because of yet another bug, the Sequencer accumulating deleted garbage, even in completely emptied files.
These should all be debugging clues to the developers if they want to solve the worst issue, the Editor Freeze, which I am sure will show up for more and more people in time.
Thank you again.