Here are a couple of things you might try if you haven't already done so.
First right click the panel choose 'Panel Settings' and make sure 'Use custom panel size' is not selected.
Second right click the panel again select 'Add Applets to Panel' and remove the 'System Tray' applet then replace it again.
They are pretty simple moves I know, but sometimes simple works.
Fujitsu Lifebook AH532. Intel i5 processor, 6Gb ram, Intel HD3000 graphics, Intel Audio/wifi. Realtek RTL8111/8168B Ethernet.Lubuntu 13.10,Ubuntu12.10 (Unity), Mint16 (Cinnamon), Manjaro (Xfce).