When you create a link to meaning, it has the same description text as ｍｅａｎｉｎｇ or meaｎｉｎｇ (with mixed halfwidth and fullwidth characters).
However, the versions which contain fullwidth characters have no tagged questions listed. This therefore looks to be a normalisation bug in the Stack Exchange software, as the fullwidth characters appear to be normalised to halfwidth in some places, but not others.
One solution to this could be to always normalise tags with fullwidth characters to halfwidth. Alternatively, fullwidth characters could be disallowed altogether as suggested in the question.