At present, Retail's Services channel is able to bypass the internal-to-game filtering system that jChat extends. All other channels can be filtered. It is unclear why this is happening but it may be due to a bug, as no other channel is affected by this issue, in any version of the World of Warcraft game.

To be clear, when a user joins the game for the first time, they are added to the Trade / Services channel which is different than the well known Trade channel. The Trade / Services channel is apparently allowed in blizzard code, to bypass any chat filters in place, should you join the offending channel.

The only solution I have to this currently is to leave Trade / Services channel