[CAUT] pitch rise

[Richard West]

With the discussion of unison drift, I have a question which may be 
related.  What is the cause for pitch rise while tuning?  I can 
understand why the pitch might fall, especially if there's a significant 
pitch change.  But I'm not talking about a radical pitch alteration. 

Here's the scenario.  I'm working on a newer or rebuilt piano with tight 
pins and still relatively stretchy strings.  I'm trying to stabilize the 
instrument, but it's being stubborn.  I'm having to be more aggressive 
with my tuning technique, i.e., in order to settle the pitch I have to 
first pull the string higher than I like in order to move the tight pin 
and then allow the stretchy string to settle back to the pitch I want.  
As I move up the piano, the pitch  behind me tends to creep higher, 
sometimes to the point I have to retune the note below.  I'm not a 
pounder, so I don't think that I'm beating the piano too hard.  I'm not 
trying to pitch raise/lower the piano, just give it a good solid tuning. 

What can I do to prevent this "phenomenon?"  Does anyone else experience 
this?  What is the cause?

Richard West