Can/should a leaf-list entry be "merged"?

Not at all, the fact that their names are similar is somewhat unfortunate. maapi_move_ordered does not do anything with key values (or any values at all), it changes position of an entry - again, this is a bit more obvious if you try that with a list, not a leaf-list. maapi_move is not concerned with entry position (and it would not change the position in an ordered-by-user list), its sole purpose is to changes key values. I hope it is clear now that maapi_move can be used both on system-ordered as well as user-ordered lists, whereas maapi_move_ordered only on user-ordered lists and would return an error if used on a system-ordered list.

Yes please, open another topic.