I can't help with the "Pacific Case", but for the UK (as Pub User hints) MATS Part 1, Section 1, para 4.6 states
"Controllers should be aware of... Code 2000 which is selected by pilots of aircraft entering the United Kingdom from an adjacent region where the operation of transponders has not been required."
Why some people set this when parked on stand in the UK I can't fathom.
G W-H