If you look into the PBP manual, you will notice that PBP does not handle interrupts like they are meant to be. They are polled. So, there is a lot of latency involved.

"Using ON INTERRUPT, when an interrupt occurs PBP simply flags the event and immediately goes back to what it was doing. It does not immediately vector to your interrupt handler. Since PBP statements are not re-entrant (PBP must finish the statement that is being executed before it can begin a new one) there could be considerable delay (latency) before the interrupt is handled."
You should get used to using assembler interrupts in PBP. Much more power and deterministic. Read "interrupts in Assembler" in the manual. Better still, use Darrels' interrupt code as suggested by rsocor01