They are also very very picky about your speed when merging on the highway. Before merging you should be up to the speed limit... but if there are cars in the merging lane they say you should wait to move? (if the lane is ending I think this is even more dangerous).
You should never make a lane change even if the car behind you is 25 car lengths away. This is because on the test you are doing the speed limit of 100km/hr... but on most highways EVERYONE is going faster so you can't lane change in front of anyone if you will cause them to break/slow down it is considered unsafe. Go figure.
The 2 other riders I talked to and did their test that day had their G licence for 10 or more years including myself and we all thought our lane changes/speed were fine...but regardless you have to do what they expect on the test.
I guess it depends who you went with- keep up to traffic speed, if they say a lane change, you do it when its safe.. So thats your call.. when its safe. Stay at traffic speed...