This addon removes the background of the default chatframes.
I'd noticed over the last month or two that the background of my chatframes still showed up when mouseovered even if I had them locked, when they used to stay invisible.
After looking around I found that it's a bug that Blizzard don't seem in any rush to fix. I found a solution on this thread on the official WoW forum. and after hashing it together and finding that it worked, I decided to upload it here for anyone else who's noticed this issue.
Obviously, I take zero credit for the single line of code this addon contains.