K-Fed Makes New Demands on Britney

Sources tell TMZ the Britney/K-Fed divorce is not over.

We're told Federline will not sign the final property settlement agreement and is saying, before he does, he wants proof that Britney can handle joint custody. But TMZ knows that Britney and K-Fed already have a 50-50 deal where each has the kids for half the time.

So, is K-Fed making a money play? Stay tuned.