A bug arising from a UI snafu: if you enter a tag, and it is less popular than six other tags that it is a substring of, then it doesn't appear in the pop-up menu, and you can't add it to your tag set.

E.g., when I try entering [tex], the menu offers get "text", "latex" and four other tag names with "text" as a substring, but not "tex".

There might be a workaround for this, but I haven't figured it out. I propose changing the scoring mechanism so that exact matches are weighted highest.