When I emerge audacious, I get the headers installed under /usr/include/audacious/audacious, I think it should be /usr/include/audacious. This is bad as some applications include these files in order to control audacious from other applications, e.g. I work on integrating audacious into the mediacontrol applet from KDE, see http://bugs.kde.org/show_bug.cgi?id=126109 As far as I see, the only change that is required to fix this is to remove "audacious" from the following line in the ebuild or maybe just remove this line completely: --includedir=/usr/include/audacious \
I just tried it, removing the line with "--includedir" from the ebuild fixes this problem.
This is addressed in 1.0.0-r1, thank you for your bug report :)