Fixed.

It also doesn't say anything about having lists. (Python version)

Second that, probably it is was an incomplete last minute injection, but still an annoying error.

Fixed. See other posts.

Good, I'm happy for you! It is always bad practice to modify the input without first copying it.

You are right about that:

an array with one direction should return the same array, since one direction cannot be reduced.

but I don't think there could be an error in the tests since 1033 guys passed the Python kata (amongst a total of 4170, the tests being the same in all languages) as you can see at the top of the page; moreover in the tests there is no array with only one direction.
It would have been better if you had given what the test printed:-)
I consider the issue as resolved but you can give the printing of the failing tests for better and further examination.