Mysterious -2 rep for non-existent downvote to my question

Question

My reputation history shows:

The post it links to, however, doesn't have any downvotes:

Neither is this downvote reflected in my https://tex.stackexchange.com/reputation (a recalc didn't change anything):

-- 2011-04-20 rep 0     = 192       
 1     16684 (2)
 2     16692 (10)

Neither does the timeline of that post reveal any downvotes:

I don't care about the -2 rep, of course, but that seems to be some bug in the reputation system or at least something I don't understand at all. Any ideas or explanations? Should this be posted/migrated to meta.so?

Answer 1

It's not a bug, the user who downvoted reversed his decision three days later, which is shown as an "undownvote" in the reputation history:

I don't know why this isn't reflected in the timeline, I guess it still uses the old, less fine-grained reputation display approach.