I made it so when you shift-select some thumbnails, you can now move 'back' to deselect what you just selected. This also remembers what was previously selected before the shift-select started, so it works basically like an undo. I like how this works, but as part of it I had to make every thumbnail 'hit' focus in the preview viewer, which is not how all selects worked before. I already find this annoying, so I think I am going to make the system more clever and add some options around this behaviour.
I think I improved the duplicate filter's zoom locking, particularly when one of a pair is portrait and the other is landscape. It should generally be more 'stable' now, but let me know if you still have any trouble.