To bring this thread back to its intended purpose, I've noticed recently that the multi quote button doesn't clear after I respond to threads. So, for example, I quoted Matt and Ed above, typed my response, and submitted. Usually, it would clear the "multi" buttons after my post was submitted, but that didn't happen. Instead, they're still highlighted, and the quoted posts come up in the reply box if I click "post a reply" (though they don't if I do a quick reply).
I'm running Chrome on Windows. It doesn't go away if I close the window or clear the cache, but clearing my browser history entirely does fix it.