I have two bones in an armature that derive their Y location from a separate Master bone. One uses a simple Copy Location constraint, the other uses a driver.
If I grab the Master bone and move it around, the two other bones' Y locations update as appropriate, though the one using the driver lags a bit.
If I reset (aborting the move of the Master bone) the bone with the driver remains stuck at its location. The bone with the constraint pops back to the original location as expected. If I then initiate another move of the Master, the driven bone snaps to where it should be and then follows again, though the lag remains.
How can I eliminate the lag of the driven bone as well as have it always update its Y location correctly? I can't use a constraint on that bone because eventually it will evaluate an expression to set its value rather than simply copying the Master's Y location.
The Blend is : here