Well... I have known this to happen if your internet drops out (mine does regularly... dodgy ISP and router)... It drops you out but sort of leaves you connected if you know what I mean....
Its like multi logging in, but you are the only computer logged in...
I dont know whether that makes sense... I know I know what I mean.... I know it doesnt provide a direct sollution but I hope it may provide some insight into what is happening.