People have also mentioned the zip-up sweatsuit as being problematic, too. I have this outfit and had a doll wear it for about a month. I had no staining problems.

I think if one lives in an area which tends to be hot and humid, particularly with no air-conditioning, or if during the winter your house is overly heated with a stove, etc. it might set up conditions for things to bleed from fabric to fabric more readily than normal.