I had another inexplicable flat with a Conti Steher today at the track.
I have had set on my training wheels since last year. The front flatted today sometime after my event and packing up to leave. Time to find a new favorite tire.
I guess I should be grateful that it didn't happen while on the track. None of the Stehers ever flatted on the track. Only when hanging on the bike rack. Weird.