I know this bug is pretty old. But for a few years, each and every chat window now has two borders. I really hoped Devs would take a look at it, but it hasn't happened yet. It makes the UI terrible and just adds cumbersome boiler plate crap: is there any settings to get rid of this uselesness?
If you like the tabs but not the borders: https://www.eqinterface.com/downloads/fileinfo.php?id=6768&page=1 (I use this one... I think. It looks just like it.)