Updates:
Status: Fixed
Labels: fixed_2_17_2Comment #1 on issue 2793 by [email protected]: Fret diagrams - end lines too thin
http://code.google.com/p/lilypond/issues/detail?id=2793 The fix to issue 2727 thought these thick lines were empty boxes. I'll revert that patch and try again later. commit 5d2bd0633d5750cb798846436edad73547a10fcf
