@AaronShep: Are you saying the KFX files do not hyphenate unless you set -webkit-hyphens: auto in the book css?
Because, unless that is what you are saying, -webkit-hyphens cannot be used to deduce that KFX does not have soft hyphens. The default value of -webkit-hyphens is manual, which means the rendering engine will break only at soft hyphens. auto simply means it will break preferentially at soft hyphens and otherwise at calculated locations. See
https://developer.mozilla.org/en/docs/Web/CSS/hyphens
As for location calculations, it is trivial to simply ignore certain characters when doing the calculation. So again, it does not prove anything one way or another.