¿Por qué no se dispara la interrupción?

Cuando el pin RB5 cambia entre alto y bajo, se debe activar la interrupción. La interrupción se produce cuando el IC recibe alimentación y no se produce después cuando RB5 se conecta o desconecta de vdd. ¿Por qué?

Estoy usando PIC16F677-I / P

#include <xc.h>
#include <stdbool.h>

#pragma config FOSC = INTRCIO   // Oscillator Selection bits (INTOSCIO oscillator: I/O function on RA4/OSC2/CLKOUT pin, I/O function on RA5/OSC1/CLKIN)
#pragma config WDTE = OFF       // Watchdog Timer Enable bit (WDT disabled and can be enabled by SWDTEN bit of the WDTCON register)
#pragma config PWRTE = OFF      // Power-up Timer Enable bit (PWRT disabled)
#pragma config MCLRE = OFF      // MCLR Pin Function Select bit (MCLR pin function is digital input, MCLR internally tied to VDD)
#pragma config CP = OFF         // Code Protection bit (Program memory code protection is disabled)
#pragma config CPD = OFF        // Data Code Protection bit (Data memory code protection is disabled)
#pragma config BOREN = ON       // Brown-out Reset Selection bits (BOR enabled)
#pragma config IESO = OFF       // Internal External Switchover bit (Internal External Switchover mode is disabled)
#pragma config FCMEN = ON       // Fail-Safe Clock Monitor Enabled bit (Fail-Safe Clock Monitor is enabled)

void main(void)
{
    // Select 8 MHz internal oscillator
    IRCF2 = 1;
    IRCF1 = 1;
    IRCF0 = 1;

    // High Frequency Internal Oscillator is stable
    HTS = 1;

    // Use internal oscillator for system clock
    SCS = 1;

    // Global interrupt enable
    GIE = 1;

    // PORTA/B change interrupt enable
    RABIE = 1;

    RABIF = 0;

    // RB5 as digital input
    ANS11 = 0;

    // RB5 as input
    TRISB5 = 1;

    // RB5 interrupt on change
    IOCB5 = 1;

    // RC6 as output
    TRISC6 = 0;

    RC6 = 0;

    while (true)
    {

    }
}

void interrupt myintrout(void)
{
    if (RABIF)
    {
        RC6 = RC6 ? 0 : 1;
        RABIF = 0;
    }
}