'Special' folders like documents, music ... (defined in $HOME/.config/user-dirs.dirs by xdg-user-dirs) are accentuated by thunar or the panels directory-menu-plugin by adapting the folder icon. It would be nice, if the places-plugin could do this as well. There is an old enhancement request (https://bugzilla.xfce.org/show_bug.cgi?id=4003) going in the same direction, which was decline due to a too strong dependency on thunar. But I think this is not valid anymore since the panels directory-menu-plugin does not depend on thunar.
Fixed in 1.6.0