Gah. π Too many edge cases with the approach that detects changes inside the range of a moved slot. I've come up with a new approach that handles all the scenarios in a much better way. Can you give it a shot in 1.6.20? I will try to upload it in 2-3 hours.
One caveat is that if a slot has been keyed, its order for that key won't be affected if you change the order in setup mode. This is usually what you want, after all you specifically moved the slot
except which slots have offsets is determined by a fancy diff algorithm and diffing is ambiguous. Eg, ABC -> ACB could be described as B+1 or C-1.
Still, I think the new way is quite robust and I'm pretty sure we won't be able to find a better way to keep animation draw order keys intact while adding, duplicating, deleting, or changing the setup pose order.