Why was there not a flag on Xue's / Xun Xun's passport?

Why can people who apparently commit child/spousal abuse like Xue still leave NZ so easily on pasports? (OK I guess he is allegedly guilty of thse things one needs to be careful)

Surely there should be some sort of automatic hold on their ability to travel with their children in light of that sort of thing at least without the other partner's agreement. Otherwise we are wide open to someone commiting a crime and abducting the child and taking them overseas. Come on surely our government departments can talk to each other.

Having said that I understand they dont talk much at all.