Alaskan Timber,
You mentioned the situation of a bleed trip off.
However, with the ISOLATION VALVE in AUTO position, the valve will only open when one of the BLEED AIR switches is selected off, the manual doesn't mention anything about a trip off.
Just like Cakov, I've been struggling with this question for a long time. I've asked several people on the line, but nobody has given me a reasonable answer so far.
Regards,
FC