The nose-wheel steering issue on the A320 family (and also the A330/A340) was a hardware problem, not a software one - although the software was upgraded on a relatively regular basis. The problem was contamination (water, de-icing fluid etc.) entering the nose wheel steering box, causing electrical malfunctions and it took Airbus several attempts before they managed to produce an acceptable design with effective sealing. During that time it became SOP to switch off the nose-wheel steering (NWS) before push-back pre-empting any issues with the NWS becoming active during the push-back, even with the steering pin engaged. Once the issue had been resolved - and it took several years for Airbus to produce the final solution - most airlines had an SOP to switch off the NWS before push-back until all their aircraft had a modified box. This makes sense in that it meant crews did not have to be aware of the mod. state of the aircraft. Once all the aircraft in the fleet were modified it then became acceptable to no longer switch off the NWS before pushback.