Taz,

Try this version with the nop just after @ SLEEP and see if this helps.
Code:
DEFINE OSC 4

CMCON=%00000111
VRCON = 0 
PAUSEus 10 
TRISA = %00000110
TRISB = %11110000   ' using upper 4-bits for interrupt
PORTA = %00000000 
PORTB = %00000001

OPTION_REG.7 = 0 
OPTION_REG.6 = 0
 
led var portA.3
 
INCLUDE "DT_INTS-14.bas" ; Base Interrupt System
INCLUDE "ReEnterPBP.bas" ; Include if using PBP interrupts
 
ASM
INT_LIST macro ; IntSource, Label, Type, ResetFlag?
    INT_Handler RBC_INT, _check, PBP, yes
    endm
    INT_CREATE 
ENDASM
 
@ INT_ENABLE RBC_INT 
 
cycle:
    HIGH led
    pause 100
    LOW led
    pause 100
    @ Sleep
    @ NOP
    goto cycle
 
check: 
    WHILE (portb >> 4) != 15
      PAUSE 10
    WEND 
    @ INT_RETURN