That's something I haven't ran into so I don't have an answer off the top of my head. I know you probably have tried this but is he using a true black or is he using CYMK to mix to make the black? I guess my question should be is he printing in monochrome or color. I've had issues with that before especially with black not being able to get dark enough using CYMK. I will do some research with my techs and update in the morning as well.