Tuning problems under capo bar

[Michael Gebhardt]

Hello everyone!

I've recently started to teach myself piano tuning. During 
Christmas holidays, I've had an opportunity to tune my 
parent's piano (1980 Hamburg Steinway A). I've noticed the 
following problem:

When I tune the strings that pass under the capo bar, 
nothing happens at first, and as I continue to turn the 
lever, the pitch suddenly "jumps" far beyond the point 
where I want to get it as soon as friction in the contact 
point with the capo bar is overcome.

In order to get a smoother change, I had to strike the note 
several times VERY firmly after each slight turn of the 
pin, to equalize string tension.

So here the question:
Since I haven't so much tuning practice, it might take many 
such firm strikes before getting an acceptable final 
result. So I ask for your opinions if this might lead to an 
excessive wear of the hammer felt (compression and 
engraving of the strings), more than say a few hours of 
normal playing.

Thanks in advance

Michael