Mark, you'll probably have to clear the transit lounge but if you're ticketed from LHR-AKL then your bags are going to go all the way through- you shouldn't need to re-check them.
Most airlines these days don't allow the transit passengers to stay on board and make everyone get off. This DOES require you to be re-screened as no one trusts anyone elses screening. That happens in all Aussie ports and every international port I've flown into (HKG, FRA, LHR, FCO, SIN, BKK, LAX, AKL, etc, etc)
So, I think it's a terminoloogy thing. My suspicion is that you will only have to take your transit stuff off and go through security again in LAX and your bags will stay nicely downstairs.
Hope that helps.