What happens is something like this;

Declaring T1 VAR WORD BANKA SYSTEM creates a user VAR T1 without the underscore. Then you can use T1 in your assembler routine without the underscore like in my example.

T1 VAR BYTE BANKA removing the SYSTEM part would create the user variable with the underscore _T1, which wouldn't clash with the PBP temp system variable T1.

I.E. the user var would be _T1. PBPs system var would be T1.

A good rule-of-thumb would be to just never declare a system variable with any PBP system variable name. Totally my fault on this one. I did this for someone that asked me to translate a Microchip Tips & Tricks example to PBP, and just didn't consider T1, like used in the Microchip example.

Maybe it wouldn't be a bad idea for the PBP manual to include a complete list of all temp system variables?

Standard PBP system variables are listed in the reserved words section, but none of the temp variables, that may or may not even be used, for heavy number crunching are.