I don't know if this is a regression in 1288 itself, or specifically related to (dup) highlighting,
but (at least with highlighting enabled - didn't check otherwise), (video) Length Property is
(again) distinguishing ms when determining "duplicates".
(At least I suppose that is what is now happening in 1288.)
So if you have two files,
1. 46 min 0 s 667 ms
2. 46 min 0 s 720 ms
they are not (colored [highlighting]) as duplicates (in 1288 [where they were in 1286]).
(Above is the short version
