During 1.08 or so the lines in chat had a semi transparent black background that made the text readable on any surface. I believe the ob port broke this and it was never fixed.
There was a hacky fix that had the background always on, people hated it so there was another hacky fix, it can be enabled with a cvar. Can't find it though. >_>
Oh, I always thought that was a bug that was finally fixed during the 2.2x releases. Never knew it was actually a feature.
