why does a string go out of tune?

[Phil Bondi]

Wim, do you listen at ppp?

I don't know about your D, the the ones I have had the chance to work 
with, and one in particular that I do care for, the pins are not the 
strong suit of the instrument..and no I'm not Steinway bashing..I'm just 
speaking of 1 piano with similar characteristics of the one you speak of.

Do the pins of the falling unisons feel any different than the ones that 
seem stable? Maybe you're flagpoling into place? slightly hard hammer??

..don't know Wim..I do know I have seen a similar situation here.

Phil Bondi(Fl)