Thunder Charge buff icon - Paladin

I've noticed this as well, but there's another bug that goes along with the lightning charge there. If you're using dual charges and switch weapons, the icon for lightning stays on while the other charge goes away. What's even more interesting is that you can actually add another lightning charge on top of the the one that should have vanished, resulting in there being two lightning charges at the top of the screen.
I played with this glitch a bit, and it seems like the second lightning charge doesn't do anything to your damage ( I went to kill some lightning weak monsters and hit them for regular damage ) and even the attack swings look as if they're neutral.