Max tag length setting ignored when retagging question (but not when editing)

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I attempted to retag a question on my hosted site just now. In this case, the question relates to obtaining citizenship in a particular country, so I tried to retag it to add the residency-and-citizenship tag.

However, when I attempted to retag the question, I saw a confusing error message:

That's odd; I thought I upped the max tag length in my Askbot settings:

Interestingly, this only seems to be a problem if I am retagging a question. If I edit a question, I am able to add the longer-than-20-characters tag.