So, reciently I noticed this nasty, metallic aftertaste in the back of my mouth that never went away. My mom noticed it too, and began researching it. Turns out that some pine nuts will cause this "taste disturbance" for up to two weeks after eating them. I speak from experience that it's not a very pleasant thing to have...
So, beware of pine nuts from china. I don't think they harm you in any way, but there must be a different species that just causes this nasty aftertaste.