In Parole 0.5.90, face-sick-symbolic icon is not always available with icons theme. I think it's better to replace this icon by face-sad-symbolic image.
Hm, I'm wondering whether it's really that much more likely that face-sad-symbolic exists in icon-themes (face-sick-symbolic exists in e.g. gnome). The question is, is this menuitem-icon important enough to ship it with Parole (in case icon-themes don't have it) or is it fine if there's no icon (which seems to be ahead with Gtk3.10 in general to some extent...).
Under FreeBSD, your (Xfce stuff) default icons theme is Tango, and face-sick is not available. I know, Midori has also MenuItem to report bug, and there's no icon, it's not puzzling.
After some discussions with Sean we've decided we'll leave things as they are for the moment. The bug icon isn't that important and with the spreading of (the meanwhile released) Gtk3.10 it'll be gone anyway...