>>800
The tag in question is "2 females", so it appears in plenty of sibling pairs as the "new" sibling. That's why I clicked "petition all tags" to make sure that it wasn't just that I missed a sibling that I didn't know about being displayed as that tag.

>It seems to occur more often from tag changes by the Client API, but it does not sound like you have been using this to edit tags.

I don't even know what that is, so I don't think I'm doing any of that.

It's good that this is a bug though. I thought it might be a feature. Having tags from the PTR that I can't remove, at least in my own DB, would've been a dealbreaker for using the PTR. I can't have the PTR tags eternally ruining my searches and there being nothing I could do to fix it for myself at least.