The IRS has their rules, and like it or not we have to follow them. One issue is that whatever a divorce decree may say may not matter. The only authority that can over ride the IRS rules is a federal judge or congress. Since federal judges don't deal with divorce, separation or custody issues, I don't see that ever happening. A lower court judge can "rule" whatever they want. But it holds no weight with the IRS.
Now when it comes to state taxes, that very well may be a different story. But with federal taxes, I've never known the IRS to "heed" to a lower court order. I'm not saying it hasn't happened. But I've never seen or heard of it.
I would suggest you question what I've stated above, with your legal advisor on this. The four most powerful words in your arsenal will be "show me in writing". I've never found, heard of or seen any IRS statute, publication or congressional law that requires the IRS to break their own rules in order to comply with the ruling of a lower court.
