Hmmmm..... I upgraded my main laptops Arch packages last week to 4.3 and since have found an anoying bug. It seemed that whenever I rebooted I would have messed up panels with widgets in a different order to when I shutdown, panels that where centered to the left and a System Tray that could and would appear anywhere.
After much playing around I think I have nailed it down to the Plasma default theme, Air. It seems that if you apply a different Plasma theme the problems vanish. I'm not sure if this is a known issue or not but if anyone does know anything I would be interested.
I will try and get on #plasma tomorrow to speak to the guys and find out if it is a known bug and if not file a bug report.