This may or may not apply to your situation, but years ago I had a similiar problem with Spinergy long-stemmed tubes. These had threaded stems, and the flats arose because I had overtightened the nut on the stem which exacerbated rubbing between the tube and the valve hole. I just stopped using the stem nut and the problem was solved. YMMV.
Ray Plotecia said:
Is anyone else having a problem with flats that occur with long-stemmed Continental tubes? They tear right where the stem enters the tube.
Or is it just me after 35 years of cycling and fixing flats?