What I suggest is removing the standard from the rail, remove the scales (rulers) from both sides, remove the guide rails, the front one has the gear track for movement, and the movement knob with shaft. Thoroughly clean all parts in degreaser/solvent, apply a thin coat of light weight to medium weight grease (most bicycle grease will work fine) and reassemble. The lock on mine does not work that well but the knob has enough tension to prevent accidental movement of the standard.
Another thought, did the shift knob lock get jammed in the lock position? If so it would cause the problem you are having.