Kevin Federline is refusing to sign his divorce papers because he's concerned about Britney Spears' recent behavior, and wants proof Britney is able to handle joint custody of their children. A source tells People:

"Britney's attorneys are anxious to see Kevin sign off on a divorce. But Kevin and his lawyer Mark Vincent Kaplan are dragging their heels out of concern over reports of Britney's post-rehab partying. [Federline] wants to make sure that the divorce document makes it simple enough ...