Ljmp 0 = ljmp 0, nothing else. On a power-up all sfrs are set to the value shown in the data sheet (at least the Philips data sheets) on ljmp 0 they stay at the values they have. If you need a reset use a derivative with a watchdog and let the watchdog time out.
In the olden days before the puppies were born, I coded a '51 to set all sfr's to the power-up value on a jump to zero, you can use this method if you have to.

Have fun,

Erik