Yes, it's a bug.
It breaks many commands such as /whisper, /ban, /report, /squelch, etc.
Additionally, it allows you to spoof as other players, as well as create weird combinations of names which historically have never been permitted.
Knowing Blizzard's track record though, I have no idea when this will be fixed. As I said, it could be mid-season or any time. Just be prepared to lose these accounts at any time without notice.