My two year old was able to pull mine out of gear as well. I have not been able to duplicate this condition.
I have noticed that my shifter does not seem to align with the indicator or the detents that are felt ( when shifting to reverse I have to shift slightly past the reverse position to get the transmission to engage). I suspect the shift linkage is out of adjustment on mine. If this is the case, it could keep the shifter from fully resting in the home position and prevent the lock pin from engaging.
I'm going to investigate this further, I'll let you know what I find. | 
