This also affects me on a fresh install of xubuntu-14.04.3-desktop-amd64 with all updates.
The command xfce4-panel --version reports "xfce4-panel 4.11.0 (Xfce 4.10)".
A workaround that seems to have fixed it for me is to insert a separator as the last item in my panel (to the right of the "Action Buttons" item).
This also affects me on a fresh install of xubuntu- 14.04.3- desktop- amd64 with all updates.
The command xfce4-panel --version reports "xfce4-panel 4.11.0 (Xfce 4.10)".
A workaround that seems to have fixed it for me is to insert a separator as the last item in my panel (to the right of the "Action Buttons" item).