On forums I read it could be because gtk+ version... x11-libs/gtk+-3.22.16 xfce-extra/xfce4-pulseaudio-plugin-0.2.4 but all versions fail 0.2.5, 0.3.1 as well.
Duplicate of #13898 https://bugzilla.xfce.org/show_bug.cgi?id=13898
Duplicate of the above. *** This bug has been marked as a duplicate of bug 13898 ***