OK, so after discussions in chat about the future of sbs-2008, I created a tag synonym the wrong way, from sbs-2008
<-- windows-sbs-2008 . Realising I made the wrong one, I went to the mod tools and hit "swap". Everything reflected correctly in the Tag Synonyms console, so I merged the two tags together.
Now, everything seems broken. windows-sbs-2008 redirects to sbs-2008, which is empty and doesn't exist, and is showing 0 questions (correctly).
Official SE team: Halp please!