The core functionality of the Edit button has not changed, and you can make tag-only edits within reason.
I have previously encountered situations where I only wished to change a tag, but the edit was "too minimal". That said, I was able to submit an edit to a question where I only removed the unityscript tag1. I was required to submit a manual edit description, but once entered, my edit was successfully submitted.
It is difficult to define "too minimal" in regards to a tag-only edit, due to conflicts between the two circumstances, but here are some ideas:
It may involve further consideration, regarding edited characters
- It can not be a simple count of how many characters the edit changes, as an edit of "legal
game-design" has a character count of at least 16, while " unityscript" only has a character count of 11.
- I had considered that only the 'total character sum' of tags was taken into consideration, but by my count, "legal
game-design" gives a 'total character sum' change of +6.
It may be an unwritten privilege
Admittedly, the ability to make tag-only edits might seem insignificant. As a result, it is entirely possible that the ability to do so comes with the provision of other privileges, without deliberate mention. If that is the case, this would have to be somewhere between the last privileged you unlocked (View Close Votes at 250 reputation) and the next privilege I can unlock (Edit Questions and Answers at 2,000 reputation). Two particular privileges stand out:
- Create Tags at 300 reputation may also yield improved ability to edit tags.
- Access Review Queues at 500 reputation may also extend the general ability to edit, including tags.
Either way, nothing is mentioned regarding editing tags. We would need a moderator or higher to comment on whether either of these could or would be the case.
It may be a user-specific bug
If it ultimately boils down to a bug, we know that the bug does not affect everybody, or is at least a little more specific than preventing all tag-only edits. We do know that it is not a recent change, as ultimately, we have seen that tag-only edits have been accepted as recently as within 5 hours of the original post.
1 Immediately after submitting the tag change, I proof read the question and submitted a more thorough edit. The initial edit was confirmed almost instantly, so both edits appear as separate revisions.