Earlier today, a diamond moderator created a new question, and also created a new tag to go along with it.
It happens that the tag already existed, only with hyphens. I've corrected the mistag.
If you're just tuning in, we've historically had a problem with people creating duplicate tags that differ only in hyphenation. The system was modified a while ago to detect such possible duplicates and will force normal users to use the existing tag instead of creating a new one.
Moderators are exempted from this restriction so that existing tags can have their hyphenation changed via synonyms and/or mass retagging.
This exemption should not be extended to the new question form, as it seems to be now. It will be one less way for people to shoot themselves in the foot.
This question if you're curious.
e: It also happens during editing, though that is working as intended...