Kawai piano needs orthodonture

[Tvak@AOL.COM]

Last year, I helped some good friends of mine find a piano.  After a couple 
of months looking, I found a Kawai console which they purchased last January 
(2001).  This piano dates back to the late 70s with one owner, a professor 
and musician;  the instrument was in very good condition with little hammer 
wear.
    I tuned it for them and did a full regulation of the piano, including 
setting key height and key dip.  Now, just 13 months later, the keys are not 
level any longer.  And I'm not being picky here, this keyboard looks like it 
needs orthodonture.  I would expect a leveled keyboard to last for years 
before it needed leveling again.
    What would cause this?  
    I can guarantee there are no children banging on the keys, as the parents 
are professional musicians and I am confident that this would never take 
place in their home.    The humidity level in their home is at 21%, which 
seems very low to me, but then, I leveled the keys last January when the 
humidity was probably close to the same.
    This piano also goes out of tune amazingly fast in spite of the pins 
being tight in the block.   I can see why it would be out of tune from my 
last tuning in August, now that the humidity in the home is so low, but I 
tuned it one week ago and today there were 3 or 4 unisons which had drifted 
dramatically.  This is not a one time event, either;  I am always 
disappointed when I visit them to find how poorly the piano has held its 
tune.  
    The piano itself seems fine to me.  The work I did on it is the same work 
I've done on other pianos.   I have mentioned to them that the low level of 
humidity was not good for the piano and could possibly be causing these 
problems and I got the fish-eye.  I'm afraid they think that there's either 
something wrong with the piano, or me, and they're leaning towards me on that 
issue.
        Could the low humidity be at the bottom of all of this?  The piano is 
NOT near a heat vent, it's even sitting on an inner wall.  There is a fire 
place across the room about 10 feet away.   They use it frequently. 
    What's going on here?

Any thoughts are appreciated.

Thanks,
Tom Sivak