When you upvote answers on the web version, the up arrow becomes orange (or some variation on other sites) to show that you've already voted. Here, it does not happen, so I have no indication that I've already voted. The arrow looks exactly the same as before I voted. This often makes me think I haven't voted, so I vote again, and get the error banner. This is frustrating and has happened many times. Please make the voting arrows indicate that you've voted.