Being a Bus diver and not a Boeing Engineer, here is a sketchy outline view (RUMOUR) of what I was told happened.
Apparently the said aircraft required the landing gear selector unit (ie the gear lever quadrant) to be partially or wholly replaced. Problem was that as the gear wasn't actually being directly worked on and hence the required pins were not in place. As the new equipment was being replaced, not noticed, the selection of the new equipment was at UP, CAUSING GEAR RETRACTION!!
Rumour not fact but most likely very correct form a good source.
Cheers GD
