That was always going to happen, as a vast majority of the people that have keys at the moment are commuters, so they will take one at the end of the day to either a rail way station / tube station or to where they live. TFL/SERCO stated this before hand and a fleet of electric vehicles that could move the bikes around was mentioned. This is also a reason why it isn't open to general use as well.
Why's that a reason for it not being open to general use? I'd have thought that general users might move the bikes back around after commuters had left them in the centre of London in the morning.