AceShowbiz -

The divorce settlement between Britney Spears and Kevin Federline won't reach final anytime soon as he has refused to sign the papers, claiming he is worried that Spears is not responsible enough to take care of their children, Sean Preston and Jayden James.

While "Britney's attorneys are anxious to see Kevin sign off on a divorce," "Kevin and his lawyer Mark Vincent Kaplan are dragging their heels out of concern over reports of Britney's post-rehab partying," a source close to the couple revealed.

It is said that K-Fed believes that Britney is "mentally unstable", and thus wants proof from her that she is capable of handling joint custody of their two sons. He "wants to make sure that the divorce document makes it simple enough for Kevin to downsize Britney's access to her kids the next time her behavior troubles him," the source went on saying.

Kevin and Britney both have reached an early divorce agreement in March which allowed them to have custody of their two sons. Meanwhile, the troubled singer has been seen hitting the nightclub quite often recently following her release from rehab in March.