Holden Astra 2008: Why did the steering lock while driving?

The steering on our 2008 Holden Astra CD hatch locked up while our son was driving. Thankfully it happened at low speed, but had it happened at high speed it would have been dangerous. After towing the car to the nearest Holden dealer the electric steering motor was replaced. I have tried to find out from Holden if this is a common problem that could happen again, but they will not discuss this other than to say the usual company dribble about the repairs are covered under warranty etc. I am only interested in knowing that a failure such as this is a rare occurrence and the car is safe to drive, but they will not give me any answers. I have found Holden service and customer interaction to be less than acceptable throughout my ownership of the car. Have you heard of similar issues with Astras of this vintage?