Austman,
I’m not familiar with Vic and ACT laws.
But if you look at NSW doors, the sliding pane is always on the inside of the centre line, and the fixed pane is always on the outside of the centre line.
That’s if you want to get that pedantic.
In my experience, sliding doors get misaligned (and fail to lock) for two reasons:
1) The rollers are worn (or flat) and should be replaced. Cost $100-$200.
2) The whole building has become infinitesimally trapezoidal due to subsidence. This might be fixable by adjustment of the roller height. Cost $100-$200.