Do you have any battery rattle when its assembled? If not, check the switch contact, specifically the one that turns when you turn your 69's switch to the "lock" position. If that contact is not centered try centering it and see if that helps. If it doesn't, take a look at where it makes contact, you may need to move it slightly up or down to make contact with both sides.

When the switch is depressed that contact completes the current between the pin above it and below, so see if is not touching one side.
If you don't feel like adjusting with the pin by opening the switch, first turn it one direction to lock, and again in the same direction to unlock, this will switch the lengths from one side to the other. Though if the quick way doesn't work and that pin
IS your problem, you will still need to to adjust normally.