Grease Spots?

Check the fabric content of the clothes that get the dark spots, if the fabric content is mostly polyester these spots appear. It seems the polyester draws dirt from the other clothes. Try washing them separate from other clothes that are not mostly polyester. This should solve the problem. Hope this helps.
D.

I hsve this problem too. Thanks for asking and I'll be reading the responses.

It may be fabric softener. If you put it in either with the little Downy ball or while the rinse cycle is starting, some clothes that may be dripped on will get little spots. When you wash again, it comes off. I get this occasionally. You could try putting in the detergent while the tub is filling up, before adding the clothes and for the rinse cycle add the softener after the water fills a bit if that is an option. Though I think that depends on what kind of washer you have-not sure how these new front loaders work.

Thanks for the question. We get the same problem and maybe it is fabric softener like the other person suggested. It's just a pain to have to wash the shirts that get the spots twice.