[wt200999]

if you look in the default code in the interrupt handler

  else if (INTCONbits.RBIF && INTCONbits.RBIE)  /* DIG I/O 3-6 (RB4, RB5, RB6, or RB7) changed. */
  {
    int_byte = PORTB;          /* You must read or write to PORTB */
    INTCONbits.RBIF = 0;     /*     and clear the interrupt flag         */
  }

PORTB is the register. You have to read/write to it before you can clear the flag. Have a look at how Kevin does it in his encoder code, and do you know bitwise operators and the such?