the \Hy@raisedlink (used because of what explaned in this answer: https://tex.stackexchange.com/a/17138/7712) seems make trouble with hyphenations.
Cf this MWE
\documentclass[a4paper]{book}
\usepackage[a4paper]{geometry}
\usepackage{polyglossia,fontspec,hyperref}
\setmainfont{Linux Libertine O}
\setmainlanguage{greek}
\makeatletter
\newcommand\test{6. Καὶ δὴ τῷ κράτει
\edtext{τοῦ} \edtext{συγγενέος} \edtext{ἐπιθαρσήσας}, \edtext{οὐμενοῦν}
\edtext{εἴ τι}
καὶ \edtext{δέοι}
παθεῖν
δείσας
καλὴν ἑαυτῷ
τῆς εἰς Χριστὸν πίστεως, τὴν ἐν
\edtext{Γράμματι}
νομοθεσίαν,
ὑποβάθραν
\edtext{προύθηκεν}.
\edtext{Περιτυχὼν}
γὰρ
\edtext{τῶν}, \edtext{Μωσαικῶν}
\edtext{βιβλίων},
καὶ
\edtext{τῆς Ἐβραίων ἁπάσης Γραφῆς},
καὶ τούτοις ὡς μάλιστα φιλομαθῶς
\edtext{ἐναπασχολήσας}τὸν νοῦν, καὶ
\edtext{ὅλος}
\edtext{ὅλῳ}
στοιχειωθεὶς,}
\begin{document}
\section{Good}
\def\edtext#1{#1}
\test
\section{Bad}
\def\edtext#1{\Hy@raisedlink{}#1\Hy@raisedlink{}}
\test
\section{Better}
\def\edtext#1{\Hy@raisedlink{}\hspace{0pt}#1\Hy@raisedlink{}\hspace{0pt}}
\test
\section{Ok?}
\def\edtext#1{\Hy@raisedlink{}\hspace{0pt}#1\Hy@raisedlink{}}
\test
\end{document}
The \edtext without \Hy@raisedlink produce good hyphen / , not with \Hy@raisedlink. The version suggested by @Ulrike Fischer are better, but not so good. Idealy, all line should be as in example 1, without \Hy@raisedlink{}.
\hspace{0pt}to allow hyphenation in the "rest of the word":\def\edtext#1{\Hy@raisedlink{}\hspace{0pt}#1}– Ulrike Fischer Dec 07 '15 at 17:05\Hy@raisedlink{}? And why has it an empty argument? – Ulrike Fischer Dec 09 '15 at 17:01\Hy@raisedlinkallow to add an anchor linked to the top of the line, and not the bottom. The argument is empty because it is a MWE, but normally it contain a\hypertarget{anchorname}{}. Cf http://tex.stackexchange.com/a/17138/7712 – Maïeul Dec 09 '15 at 20:04