I hope that you and your family have a nice Thanksgiving as well. I am here in New Orleans for Thanksgiving, and enjoying all of the family and good food.
I'll have my folks speak with the local Sherwin-Williams representative. I know what you mean about mildew and mold and moss growing on everything down here. I think that maybe some of the people have it growing on them as well! ;-)
That flat paint thing is weird. The only thing that I can think of is that perhaps the paint back then had some type of additive that they don't use now. Also, I guess that flat paint breathes better than gloss paint, but overall it still doesn't make sense.