On this post at Math.SE, one sees that it is tagged both with (multivariable-calculus) and (vector-calculus). If one clicks on the (vector-calculus) tag, one gets redirected, correctly, to the page for (multivariable-calculus), as for a long time the (vector-calculus) tag has been a synonym for (multivariable-calculus).
Problem: why does the post still contain both tags, instead of them collapsed into one?
What caused this:
- Mark and merge (tag-2) as synonym to (tag-1).
- Given a question tagged with (tag-1) and (tag-3), merge (tag-3) into (tag-2).
- Question is now tagged as (tag-1) only. All questions previously tagged under (tag-3) is now tagged (tag-1) instead.
- Questions tagged with (tag-3) now is tagged with (tag-2), which displays as a different tag from (tag-1), but links to the same page.
- (tag-2) now appears in the Tool panel for "new tags" as a new-tag, even though the link that it creates points to (tag-1).