[ Ref. 241020 MMDigest

Yes, there are piano keys intentionally weighted that way, more
commonly on European built pianos. Player actions seem to play
a little more smoothly with the key lock on, as the keys being
weighted to fall when the player engages the notes. Therefore,
there is resistance on the down stroke from the key.

When key locks are engaged this resistance is eliminated for
the equation. Try it sometime on your foot pumper and see if you
notice the change.

Leave the piano alone; it is a cool old thing built that way,
so enjoy that design rather than messing around with it.

Ben Gottfried - Ben's Player Piano Service
Richfield Springs, New York
https://bensplayerservice.com/