Isn't there an issue with their computer system or flux system caused by magnetic interference (or something like that) on a few of the taxi ways ie:B4...etc. There is some blurb on the Syd Airport chart about it which is why they hold so far back from the holding point on those 2 intersections.....
If they taxi up to the mark they end up with some sort of system failure.
I have flown with a few ex-Dash 8 pilots who have mentioned this issue.
This might explain the denial of ATC’s request to move forward..Maybe?