This timeline doesn't show anywhere that I removed a question downvote on the 6th. Instead, it appears to simply remove the original downvote from the calculations. That's unfortunate, since the votes shown aren't going to be especially accurate: it's impossible to tell that there used to be more sentiment one way or another than at present, and it's therefore difficult to properly judge the effect of edits or answers.
This behavior persists in the new timeline view. (The old timeline view was less clear, and may have been inconsistent in showing the original votes but not their removal.)