The 206 was the original Partner. Could be used by itself or with another to expand to 4x12. Later the 206E was introduced with the Partner Plus and Partner II. That was a straight expansion module as neither the Partner Plus or II had any provisions for lines or extensions. The 206EC enabled CID and that came along with the introduction of the ACS. Then came the 308EC. No, I believe it was an early release of the 206EC that had that problem.

-Hal