We had this same problem.  We had control over everything, too. We stopped using Sta-On, etrc.  ANd we still had the problem  - haziness, it looked like the mucin was staining, but we also had the fuzziness on non-GI's as well.  It turned out to be two things--the hematoxylin we were using and the timing of it and the temperature of the water on the stainer--it was too cold.