In many places around the world where people use Stack Exchange sites the Internet is a bet more flaky than it is in the SE offices.
Quite often I load a page and in the time it takes to read the connection has a hiccup, which I find out when I click to vote on a question, answer, or comment.
But there is a UI inconsistency and bug!
If a vote on a comment fails I get a warning box that something went wrong and the vote is reverted in the user interface.
But if a vote on a post (question or answer) fails I only get the warning box. The interface still reflects the vote even though it didn't actually go through!
This is particularly bad when you have a bunch of tabs open, which is a good way to use a browser when the connection is slow or unreliable. Because when you switch back to a tab with a failed vote to a post it looks like it succeeded so you won't know you need to vote again... But for votes on comments you will always see which votes registered.