As others have indicated, the instructions should specify required allowances for spacing, punctuation, and case.

I think you need to state that the function should return the words in the same order as they are found in the sentence. The first method I tried didn't use a stable sort, so I was wondering why my solution didn't pass even though it was returning the correct words.

It would be helpful if you explicitly stated in the kata description that case and non-alpha characters are disregarded in the palindrome test.