I know exactly what you mean zmanzorro. There's no other way to describe it except soapy.
I believe they've quietly changed the recipe sometime in the last couple years. After drinking Blue Moon forever, it's become almost unpleasant.
If you make the Nilo Blue Moon clone from this site, it doesn't have that off-flavor. Just, delicious Blue Moon, just like it used to be.
I've never had a soapy flavor in a homebrew, but I've heard it's from keeping beer in the primary too long. I very much doubt that's BM's problem.
If I ever did have a homebrew with a soapy taste, I'd start by looking at the yeast. Maybe some fats in the yeast, breaking down, or combining with other ingredients to make a soapy compound.