Option to disable autoscroll when scrolled up

The way the autoscroll works now is absolutely infuriating if you're in a quickly-moving channel trying to read something just offscreen.  You can use the scroll wheel or Page Up to scroll up to read something, just for a new message to shoot you straight back to the bottom mid-sentence.  There should be an option to make the chat only scroll if you're literally all the way at the bottom completely caught up and not scroll if you're even just one message above the bottom.  Please, let me read stuff that's only barely off-screen without having to scroll back up every other word!