A few minutes ago I went to Stack Exchange to see the Top Users for Stack Overflow and found this:
Hans and David are displayed twice.
I can't reproduce this any more either.
I just gave the code a quick readthrough, but the culprit didn't seem obvious. (As Nick noted, we made some network changes over the weekend, so the underlying problem is likely that certain private APIs that leagues depend on were made unavailable at times.)
We'll keep an eye on it going forward.