While editing my watched tags list on RPG.SE, I received an unexpected error message saying that "gm does not exist on this site".
The reason why the error was so surprising was that I never had
gm on my watched tags list in the first place (and no, I wasn't trying to add it, either). What I did, however, have among my watched tags was the wildcard
gm-*, which would match any of the several tags on the site beginning with "gm-". However, now (after adding a completely unrelated tag to the list) it was gone, and trying to add it back just yielded the same error message.
A little more testing revealed that this issue affects all SE sites, and that it does not actually depend on whether the "base" tag exists; rather, the SE software simply strips away the wildcard (and the hyphen) from all tags when editing the watched tags list.
For example, trying to add
java being added instead. Also, trying to add
*script (because I also really like all scripting languages) just yields the error "script does not exist on this site". And trying to narrow it down to just
j*script yields the even stranger error "j script does not exist on this site" (yes, with a space in the "nonexistent" tag name!):
Anyway, watching or ignoring wildcard tags used to work, so this is a regression, and I haven't been able to find any statement that it would be intentional.
I suspect this regression occurred as a side effect of the changes to favorite tags a few months ago, but none of the answers in that thread mention it, and it's been long enough since that announcement that it's better to report this as a separate bug.
Of course, as a work-around, I can just manually expand the wildcard and add all the matching tags to the list. But in some cases (e.g. language tags with lots of version-specific variants, like, say,
c#-*.* on SO) this can get pretty awkward, especially since the automatic dropdown shows only a limited number of matches.
Ps. An easy way to reproduce this bug is to try to watch (or ignore) the wildcard tag
status-* here on meta. Currently, all you get is an error messages saying that "status does not exist on this site".