This seems like it might be a reoccurrence of an old problem, but it seems to be a variant this time. In Pathfinder in version 6.01.08, I'm finding that creatures with innate spellcasting capability mirroring sorcerer levels (e.g. rakshasa, dark naga) who take actual sorcerer levels spontaneously gain a higher caster levels every time they're saved and reopened.
The first time a character is saved and reopened, it might be okay and there's no caster level increase. However, after that, each time the character's reopened, the number of levels
I've duplicated this with a Lammasu (natural oracle casters) with oracle levels (while testing out some unrelated fixes in 6.1.09), so the problem doesn't seem to be unique to the sorcerer entirely. However this time though, the problem doesn't seem to replicate with non-spontaneous casters no matter how many times I save and reopen (eg. drider cleric, drider wizard, nymph druid).
Blargh, just as when I think I've got the patten down, I do some more testing and find out that you don't even need any levels in the casting class, the base creature if you open and save it enough will begin gaining caster levels. So that Rakshasa doesn't need a level in Sorcerer for this to happen. The act of saving and opening a spontaneous casting monster (ie one that casts like a sorcerer) seems to be the thing to trigger it.
This can be seen in the PCG file, with
after a save/load cycle.
I've fixed the issue (again) with characters getting extra caster levels on load. If you already have character with duplicate caster levels, the RACE line in the PCG file will need to be manually edited to remove the duplicate.
I have also added a unit test to pick up any recurrence of this issue.
Tested this fix with a base rakshasa, rakshasa with class levels, a lammasu, and a kirin, and they all seem to work fine without getting more caster levels.