[Bug] Upvotes and the back button

So if I enter a thread, upvote the OP, then hit the back button on my browser, it appears like I haven't voted yet.

Here is where things get interesting. When I go to upvote, the number updates, but the arrow goes to neutral. If I upvote again, it raises the number again.

Don't know if this is purely graphical, or if this is exploitable.