xfce - pinned applications have wrong bg, instead of panel bg given

[markoER]

after gnome3 comes out I like many others switched to xfce.

Description is in follow,
when application is is pinned to panel, it has wrong and unusal background, which is not taken form gtkrc at all, so no metter if i change global theme. This bug is tracking me for some time in xfce, it is not affected just in latest release, all releases has this behavior. hex code of wierd bg is #333333.

to conculde this, other things like preferences, theming, showing active/inctive windows works great. If i place panel bg to some pixmap, my pinned application will have weard look, so i can only use flat panel with color #333333 if i dont wan't to see ugly square for pinned app.

You can see in attachment what i am talking about