Yes. The fact that he can claim him on his taxes will not change until there is a NEW order saying otherwise, one "in the works" does not count. Since the year is over, your ex gets to claim him, as it says in the decree, end of story.

Now, the back support is a separate issue. They may take his refund (or part of it) and apply it to his arrears. This is regardless of whether or not he claims the child.

I would call CSE and ask what will happen if your ex gets a refund but is in arrears. Make sure your account is accurate with them.

Good luck.