Yesterday during a GIG I had a couple of clips that at first decided to exchage thumbs by themselves.
Then I noticed that they also had copies and/or mirror clips, loaded into the composition as well.
When I tried to delete one, the mirror was also deleted. Reloading some clips into the same composition slot, recreated the mirrors. Changing the thumbs also updated the mirrors. Selecting one also selected the mirror.
Today, I had another GIG but no issue were reported.