Sound repeats every time a new tab is opened even after acknowledging chat in other tabs

When a user sends another user an IM, and sound is enabled, the user receiving the IM will hear a sound when the IM box flashes, as expected. However, I find that if the user then opens the IM to acknowledge the notification that there is a new message, and then that same user opens the site in new tabs, they will hear the notification sound play again and the chat box will flash as if there's a new message.

It seems like the server doesn't recognize that the user actually acknowledged the message.

I'm using the Normal AJAX method, with Firefox 25, and no Node JS server.