Dependent for half a year?

I have a friend who is 18 and still living at home with his parents. However, up until september, he was paying his own way with miscellaneous, untaxed jobs. Then he got a job in September and grossed around $15,000 (taxed) by the end of the year. However his mother still wants to claim him as a dependent because he's still living with her. She's telling him that she can claim him as a dependent for the first half of the year, and then he can file himself for the last four months. I've never heard of this and personally, I think she just wants another tax exemption. Has anyone ever heard of this? What do you think he should he do?