CLP(ℤ) not monotonic

Please consider [**`riderhorse.pl`**](https://www.metalevel.at/prolog/scryer/riderhorse.pl), based on solution generously posted by @david-sitsky in https://github.com/mthom/scryer-prolog/discussions/3341. With this program, we get: <pre> <b>?- f(RiderHorse, HorseRider), HorseRider = [6|_], labeling([ffc], RiderHorse).</b> RiderHorse = [4,2,5,3,0,1], HorseRider = [6,2,4,1,3]. % expected <b>?- f(RiderHorse, HorseRider), labeling([ffc], RiderHorse).</b> false, unexpected. </pre> I would greatly appreciate any help to reduce this to a smaller fragment that exhibits the issue, and to find the reasons that cause this. @flexoron, @notoria and @haijinSk, I hope this is especially interesting for you, thank you a lot!