Disklavier

I took my sister (who plays piano for 30+ years) to a very nice 
dealership in the Bay Area to check out MPX1Z (48" upright Disklavier 
with silent mode) and MX1Z (48" upright Disklavier w/o silent mode), 
both based on the U1. She noticed the keys are stiffer when the 
Disklavier control deck is powered on. The keys become stiffer and 
she needed to labor more. Not expecting this, I did a blind test and 
she always knows when the power was on. 

We also tested the U1 and it was free of the stiff, heavy feeling she 
sensed. We went back and forth among the three and roughly concluded 
the U1 has the "cleanest" action followed by MPX1Z (Disklavier off), 
MX1Z (disklavier off), MPX1Z (Disklavier on) and MX1Z (Disklavier 
on). The action feeling of the MX1Z was so stiff that she could not 
recommend it.

Are the pianos not properly set up?  Can anybody shed some light on 
what have we encountered? I do not play but did some research towards 
our pending purchase. I know many people has mentioned the silent 
mode changed the action due to a shank being moved in to block the 
hammer. However, I do not recall any comments on the Disklavier 
mechanism as a whole that changes the action feeling (for the worse) 
vs. a U1.  Should these Disklavier uprights based on the U1 play 
differently than the U1 at all?  Any Disklavier guru out there, 
please help!

Thanks,
Bin