A "sort of" work-around is to continue to highlight text until the chat window stops scrolling, then right-click. You will almost certainly get more than you want but you can backspace to delete any extra text.
Even though it's still possible to copy text that is above the current chat window view (scrolled up) I agree that this is not fun. I'd love to have an option to turn off the auto-scrolling chat text.
Even worse, if you're trying to view text by scrolling up and someone else (ANYONE else) says something in any of the chat channels you have enabled, the chat window immediately scrolls to the bottom. With multiple people talking it's nearly impossible to scroll up to find what you're looking for until everyone shuts up for a while. There's another "sort of" work-around for this too, but turning off auto-scrolling (even temporarily) would prevent this frustrating experience too.
