It doesn't even really have to be AJAX. You could solve the problem just by setting up an #anchor so that when the screen reloads after voting, it just the user back to where they left off.
Normally I hate "me too" posts, but I feel this feature is important enough that I wouldn't want you to think other people didn't agree. Thanks.
[1] It pains me to advocate breaking the "show me exactly what I was just seeing" semantics of the back button, but I think in this case the user clearly conceives the back button as "show me the abstract resource I was just seeing."