Thanks. I was inconsistent in my use of >= and >. Making them consistent has fixed this edge case.

Also fails for

  [3, 3, 2, 2, 1, 1] -> [[3, 3], [2, 2], [1, 1]]

Here's my solution https://news.ycombinator.com/item?id=28170735

And for [1]; the "return sorted(arr)" needs to be "return [sorted(arr)]".