Howdy,This is not a bug specific to xfce4-pulseaudio-plugin but to GTK+3. You can see upstream reports in GTK+3[1], Xfce[2], and even one over at Arch[3].
If you apply the simple patch by Carlos Garnacho and rebuild GTK+3 you will no longer have this issue.
[1]: https://bugzilla.gnome.org/show_bug.cgi?id=786029 [2]: https://bugzilla.xfce.org/show_bug.cgi?id=13770 [3]: https://bugs.archlinux.org/task/55114 ~Unit 193 Unit193 @ Freenode Unit193 @ OFTC
