Pitch Raise

[Ed Carwithen]

It happened again today.  The Piano was a Schiller, circa 1908.  91 cents
flat.  I use a SAT I.  There were some broken strings (which I replaced),
so I talked it over with the owner, and we both agreed that I would tune 30
cents flat.  If the piano felt good, I would come back for a second tune in
a couple of months and bring it up to 440. I almost always tune to 440, no
matter how low it is, as it just sounds better to me, and I feel I owe it
to the customer to get it up to pitch.
  this one, however, had me scared.  So...... I reset the SAT to -30 cents,
then started Raising the pitch.  I usually bring the lower octaves up to
pitch, not above; then about C4 I start using the pitch raise function.
Generally it works like a charm.  
  Today when I got to about C6 it felt really tight.  I recalculated, and I
was raising the pitch about one whole step sharp.  I redid the calculations
without the pitch raise function, and finished the piano.  Everything from
C4 to G6 was way sharp.
  It wasn't a major disaster, but it was unsettling.  What am I doing
wrong?????
  The last time I had the problem I tuned the whole piano with the pitch
raise function and everything was so sharp that I ended up having to do a
pitch lower, and I broke several strings.  
(I do a lot of pianos that need pitch raises, and almost never break strings.)

Any Thoughts???

Ed Carwithen