I suspect the Problem 156 Luhn Algorithm checker is (partially) incorrect

It seems whenever the last two values of the number need to be swapped (i.e. 1807886091865716 needs to be 1807886091865761 in order to be correct), the checker instead believes the second to last pair needs to be swapped (1807886091865176).

You can see this here: http://i.imgur.com/AmOqg4v.png?1

Or another case: http://i.imgur.com/dvAeJgH.png?1 where the correct solution is 2960785568942304