Have to reset the interrupt flag. Usually in the PIC's datasheet, there's a little blurb behind the explanation for the interrupt bit that says something like " (Must be cleared by software) "
Code:
main:
     IF PIR1.5 = 1 THEN
     PIR1.5 = 0
     GOSUB receive_data  'check the flag
     GOTO main
receive_data:
     HSERIN [x, y, z] 'get data, flag is cleared automagically
     RETURN           'back to business