We use Zymeds Mart-1 and a dab detection system, the only time we have had a problem was with tissue that was overfixed or underfixed, our dermatopathologist does not quantitate the melanocytes, so I would suggest looking at your control tissue if the stain pattern is consistent time after time then I would have to say some other factor is the issue, such as lidocaine interference in the tissue(had this problem with giemsa staining of bone marrows) or tissue fixation (are the cases he is complaining of weekend stuff (fixing longer than 12
hrs?)If you are retrieving is the buffer you are using okay?
hope this helps.                  dana