Yahoo Hates Walmart Watch?

I subscribe to the mailing list for Walmart Watch, an anti-Walmart campaign. I received their messages in my inbox for more than six months. Then, a few months ago, they started delivering them to my bulk folder. I have designated them as "not spam" three times now. Why doesn't Yahoo recognize that I want to get these messages? I wonder if this is part of Walmart's strategy to improve their image, which includes paying some bloggers to write nice things about them on the internet.