Why does “word-definition” appear as a tag synonym?

Question

When tagging a question on English.SE, [word-definition] appear twice as a suggestion when word-def is entered.

word-definition (8)
word-definition (s)

IIRC, the (s) indicates a tag synonym. Why does this happen when,

1) a tag cannot be a synonym of itself, and
2) [word-definition] has no synonyms at all?

Answer 1

This is now fixed.