From looking up past issues of "Billboard" magazine, the format change happened by 11/15/1986. By that time, K-106 had dropped in the ratings, so a change was needed. The last thing played on K-106 was the jock jingles of all of the air talent that worked there.
Useless trivia: When Mix 106 first signed on, it IDed itself as "WMIX" on the air and did so for many years until the real WMIX in Mount Vernon, IL issued a C&D letter. Afterwards, it just went by Mix 106.5.
Robyn