Bad Power Tube?

Checked the bias on my tubes tonight and one was unusually high - .70. These are Gold Lion KT66s and I keep them biased at .45. Turn bias pot all the way down and it won't go any lower than .65. I know its this power tube because the problem moves with it. I guess the tube has gone bad somehow, despite probably less than 100 hours of use. What does this symptom say about the tube? What's likely wrong with it?
Big disappointment - expensive tube.

It's running away...Often buying power tubes that have been burned in by the seller and then matched again will lower the incidence of this occurring, but it will still happen to the best of us. An XF2 Mullard bought in 1961 for a dollar could do this and so can a reissue KT66 bought for 40 dollars in 2010. Any seller worth a web page designer should warranty the tube for 30 days. Send it back, it IS an expensive tube!

Fortunately I did buy this from a good vendor that does have a 90 day warranty and has sent me a replacement. In fact, they shipped the replacement right out without waiting for the bad tube to arrive back from me. It is indeed worth a few extra bucks to buy from a good dealer that is communicative and offers a solid warranty.