I've moved the topic to website support and let the other mods + Travis know about it internally. As far as I know it's fixable by deleting and re-adding them just on one episode (or adding them to and removing them from another episode), but it seems like quite a bunch of cast records are wrong, so that might be pretty time-consuming. Maybe Travis has a way to refresh them.

Cool, thanks! Yeah, I know of a manual method, I fixed a few this way, but there are just too many of them, scattered along the whole show.

Any update?

I'll fix it one by one when I'm back from vacation next week.

@Sheigutn said:

I'll fix it one by one when I'm back from vacation next week.

So no magic "refresh"? Bummer((

I'll start fixing them, but if there's any left by the time you're back, I'd appreciate the help.

The problem is actually much worse. At this point, I can say for sure, that the majority of the guest stars have 1 extra 'ghost' appearance. E.g. Stephanie Venditto as Nurse Brenda Previn has 12 appearances on the Cast&Crew page, but actually credited only in 11 episodes https://www.themoviedb.org/tv/1408-house/episodes?credit_id=5256cc7419c2956ff6073091&person_id=5198bf84760ee35d9a0065b5

Nevermind, fixed them all.