For the designation of the opening and ending themes, I took as a reference Animenewnetwork, which seems logical with the place of the songs on the album (1st and last track). In fact, Anison Generation put 2 Ending Themes for this movie and it seems weird to me, plus Melissa Manchester doesn't sing SLUMBERLAND CIRCUS on the album. We should be able to confirm this with someone who has seen this anime.
Links:
https://www.animenewsnetwork.com/enc...me.php?id=4287
http://anison.info/data/program/2304.html