It's worse than that. It also fails on this one:

(def board
  [[1 1 1 1 1 1 1 1 1]
   [1 1 1 1 1 1 1 1 1]
   [4 4 4 4 4 4 4 4 4]
   [4 4 4 4 4 4 4 4 4]
   [5 5 5 5 5 5 5 5 5]
   [6 6 6 6 6 6 6 6 6]
   [7 7 7 7 7 7 7 7 7]
   [8 8 8 8 8 8 8 8 8]
   [9 9 9 9 9 9 9 9 9]])

Does not work in this case (not a correct sudoku):

(def board [[5 3 4 6 7 9 8 2 1]]
[6 7 2 1 9 3 5 8 4]
[1 9 8 3 4 5 2 7 6]
[8 5 9 7 6 4 1 3 2]
[4 2 6 8 5 7 3 1 9]
[7 1 3 9 2 8 4 6 5]
[9 6 1 5 3 2 7 4 8]
[2 8 7 4 1 6 9 5 3]
[3 4 5 2 8 1 6 9 7])

It won't let me submit, but I think my solution is correct. The description doesn't provide many details, though.