That IS what it is! Seriously, that never occurred to me because I'm sure that didn't used to be something that happened, I know I've posted to comms in the past and had the other tags stick even if I put in a new one that wouldn't go through. But I guess that was long enough ago that it must have changed, because when I try posting with a sock account, none of the tags show up if I use a new tag as well. Huh, if that's a deliberate site choice that seems strange, but at least the mystery is solved! Thank you for working it out, because I wasn't at all aware that was a thing so it's very useful to know for future reference.

Anyway, yes, I have made the fandom tag for you! I try to get those done as quickly as possible, so it's usually within a day or so at the most.

Oh no, you didn't come across that way at all! Sorry, I should be the one to apologize for kind of jumping on your comment like that but I'd still been trying to work out the problem so I had a bit of a full on "THAT'S IT!" moment there, haha. But yes, existing tags only is the key. And there's no problem with the new tags, most of the reason I try to do them ASAP is that I am more likely to forget if I don't!