I found this in the new PBP3 Reference Manual on page 264

"Whenever a block of inline Assembly Language is entered, PBP sets the bank-select register to BANK0".

So, why does Nick have to manually select BANK0 using BANKSEL T1CON? It's true that all of the registers in his ISR are in BANK0. And yes, all his A to D registers are in BANK1, but why isn't PBP doing the switch to BANK0?