The RB7 interrupt flag is set based on a compare of the last latched value and the current state of the pin. In the datasheet it says "The pins are compared with the old value latched on the last read of PORTB. The 'mismatch' outputs of RB7:RB4 are ORed together to generate the RB Port Change Interrupt with Flag bit."
To clear the mismatch condition the datasheet goes on to say "Any read or write of PORTB (except with the MOVFF (ANY), PORTB instruction). This will end the mismatch condition."
You then wait one Tcy (execute a nop instruction) and then clear the flag. This is documented on page 116 of the datasheet.
So the simplest fix in this scenario is in the interrupt routine declare a dummy variable and set it to RB7 like this:
#pragma interrupt high_isr
void high_isr(void)
{
unsigned short dummy;
if(INTCONbits.RBIF == 1)
{
dummy = PORTBbits.RB7; // Perform read before clearing flag
Nop();
INTCONbits.RBIF = 0;
// rest of your routine here
// ...