WowAce

It seems to only appear on bnet messages. It will replace someones name on occasion with another btag name or unknown.

It should normally not replace someone's name with another b.tag, however unknowns are possible. Indeed, the AddOn only has access to an id when one talks to B.net friends for privacy protection reasons. The game automatically translates that id to an appropriate name if they are online, but if they aren't at the time you look at your logs, the name will be replaced with "Unknown".

There is nothing that an AddOn can do to counter this as the game itself limits the access to the real name completely.