What are some things to consider if my yeast knockout strain does not seem to be the correct mating type after I have tested my strain by sporulation or mating?

Some things to consider for the yeast knockout strains: 1.) Did you perform a PCR verification for the strain? (http://www-sequence.stanford.edu/group/yeast_deletion_project/project_desc.html#delconfirm) 2.) For your mating protocol, what is the genotype of the tester strain? 3.) Are you using any controls for the mating protocol?