Doing some test, I realized that it is the instruction:
OPTION_REG = OPTION_REG & $80 | 1 ; Set TMR0 Prescaler to 256, leave RBPU alone

which makes the DEBUG to produce garbage, as if the baud rate was wrong. This line was taken from the example of Darrel for the clock. So it seems it affects the DEBUG instruction.
Could someone explain me the root cause and how to overcome this issue.
This is my first attempt at using timer and interrupt and I am really in unknown territory here. I will keep doing some reading but any help will be highly appreciated.
thanks,
Olivier