I'm not sure what it could be that is causing that.. Ive never heard of it before anyways.
As far as expensive teas.. Revolution teas have always tasted pretty damn good and they're not nearly as expensive as some of these.
Unrelated story, One time, we had a lady call us questioning if her tea box was molded... We were tripped out, opened one at the house to discover there was a fuzzy substance inside of the bag!!

We called the manufacturer, who laughed and said, "Look, we get this a lot. They're natural teas, so the lavender flowers are trying to blossom. It happens. They're safe to drink."