The Cone 05-06 did fine you say and the Cone 5/6 disappeared? It sounds as if you fired low and the high fire glaze is underfired and has changed color only. When firing multiple temperature glazes on one piece, fire the highest temperature glaze first, then apply and fire your lower firing glaze(s). If it were reversed, if you fired high first, the high firing glaze would have been fine and the lower temperature glaze would most likely have bubbles, or may be excessively runny or have some other glaze defect from being overfired.
Thank you so much! Very helpful!