Since have done this so many times (select a region-middle clic it-drag it to another track), I suspect there is a strange behaviour in it since 5.6: everytime it’s done, region is not at the same position (sometime late, sometime early) on the destination track.
Maybe I’ve missed something in the new preferences window?
Tip to people who encounter that: in keyboard shortcuts you can assign some to “Editor/Region/Move to original position”
Audio at least.
When you middle-drag to another track the audio ends up in different vertical positions depending on the position of the cursor when the mouse wheel is released.
This happens in 5.5-749-g2d47705 but not in 5.5-592-g6de15a7