If your ex files their taxes before you and claims your child as a dependent, the IRS is going to be very suspicious when your return comes in claiming that same child as your dependent.

This often happens when a couple gets divorced and one parent has primary custody, but the other still tries to claim the child as their dependent. Or when a grandparent is the sole caregiver, but the parent still claims the child as their own.

Even if you're in the right, the IRS may force you to provide extensive proof that the child you are claiming does indeed qualify as your dependent.

"This can happen year after year, even after proving to the IRS you are the one who is correct in deducting the child," said Al Giovetti, a CPA in Maryland and a member of the National Society of Accountants.