After clicking it changes the number then changes the repective arrow back to a grey color.
Color should stay changed not revert back to grey.
Color should stay grey in situations where the user cannot vote validly for whatever reason.
Yep definitely a bug here.
It is pretty common in the Android app and will probably be fixed before 2016 so it doesn't become bothersome for other users and not become a 2016 resolution. When voting, the color should remain blue if you reload the page. If it doesn't then so something else is also buggy in the code.