I'd doing a a couple of things that may be unusual.
Firstly, my games size is larger than the size I am viewing it at - FlxGame 600x1000 viewed half size. My initial zoom is -1.
Secondly I am using 2 cameras, one for the game, one for the ui, so when I start my game state I removed all the cameras, add a new game camera, then a new ui camera.

It shows up if I leave it alone but when I try to change the zoom on the game camera I either see nothing or it gives me runtime errors - I can't paste them now as I'm at work and the project is a hobby I'm doing at home.