My ex and I had to file separate returns back in 2001 when she left. What she didn't realize was that she didn't change her W-4 when she left.
When we filed jointly, since I had the higher paying job, I had more withholding on my check than she did.
SOOOOOOOOOOOO, I got back almost all my withholding, (I had the kids) and she had to pay over $2,000 in taxes!

Funnier still, the asshole she left me for didn't give her a single penny!