Phoenix tears cure the recipient no matter what. So if the only way to heal the recipient is to turn them into the thing that harmed the person who got the wound, then that is what will happen.

The Ministry is attempting to get everyone's attention off the Triwizard Tournament's aftermath by passing a marriage law for Ancient Houses, one of them being the Potters. Voldemort sees this as an opportunity. Someone else sees it as an opportunity of a different type...