"cinchy" horses

[Laney Humphrey <laneyh@mbay.net>]

Hi All -
    Reading the posts about tenderness in the girth
area reminded me of my friend's horse that is described as "cinchy." 
He has the devil of a time tightening the cinch although it seems to be
the early part of the process she objects to the most.  Her saddle
is a brand-new Sharon Saare, fitted & made just for her and she and
her owner and working with an excellent, kind and patient trainer. 
The horse also, both owner and trainer agree, feels like she wants to buck
just when she starts to canter.  The trainer says cinchy horses often
do that because the act of cantering pulls the cinch & saddle tighter
than trotting does.
    I think I have read or heard any explanation for
cinchiness, like maybe a nerve closer to the skin than usual.  Does
that ring a bell?  Or does anyone have an explanation for it that
isn't rider related?
    Thanks!
Laney