[luatex] German hyphenation, fontspec and adjusted kerning

[Heilmann, Till A.]

(Since there has been no reply to my earlier posting, I will try to be a bit more specific this time. Also, I am not sure if this is the appropriate place to ask the question. If not, maybe someone can point me in the right direction?)

There is a problem with adjusted kerning in OpenType fonts and hyphenation patterns.

Customized kerning of letter pairs (via the FeatureFile capability of fontspec) is ignored when it coincides with a possible hyphenation of a word. As Ulrike Fischer pointed out to me, the problem seems to be the break points between the adjusted kerning pairs (e.g. between 'f' and 'h' in German words like 'aufhalten'; see minimal example below).

Is this a bug and/or is it unavoidable?

Thanks,
- Till

\begin{filecontents*}{bonum.fea}
languagesystem DFLT dflt;
languagesystem latn dflt;
feature kern {
pos f h 100;
} kern;
\end{filecontents*}
\documentclass{article}
\usepackage[ngerman]{babel}
\usepackage{fontspec}
\setmainfont[FeatureFile=bonum.fea]{TeX Gyre Bonum}
\begin{document}
fh aufhalten
\end{document}