Not sure if this is the best place for this, but anyway:

A year or so ago Nashbar was having a sale, so I bought a small pile of Continental tubes to have on hand. Yesterday, for the second time (out of 2 so far!) I had one of them go bad where the valve meets the tube - just pulled right out! Mercifully, it happened close to home, as I didn't have a spare with me.

Has anyone heard of a bad run of Continental tubes? Does this sound like a warranty claim? I'm not sure I want to use the other 8 or so I have stockpiled.

I used to swear by Continental rubber products! What happened!

It apparently is more common for presta tubes to be weak at the juncture of valve stem base and tube, due to a cheaper design. Good luck on warranty but you can try.

I've read some some people's advice NOT to use the valve nut. Others say use it but don't make it too tight. I don't use them at all and have never had a tear-out. I think their only purpose is to hold the stem while you attach a pump head during inflation. I manage to hold the stem out of the rim by pushing against the tire tread (only necessary when the tire is completely deflated).

Funny you should mention that. The first one that pulled out I was using the valve nut. But on this one I wasn't. So in this particular case, the valve nut does not appear to have any discernible effect one way or the other.

No matter what tubes I buy, I take them immediately out the box and make sure that they were not packed with a weird bend at the valve. I re-fold them to make sure there is no strain there.

I have a few 80mm presta continental tubes that I use. Same tubes now for 3 years without issues. I do sometimes use the stem nuts but am very careful with the tightness and leave them on the loose side. I am always very careful when attaching and removing the pump.

I used to leave the nuts off until I changed where I was riding and decreased my flat rate. One tube failed at the valve stem attachment, then the next one a few weeks later. I figured it was a fatigue failure from installing a pump head and switched back to nuts. That hasn't happened again in spite of not replacing tubes for other reasons.

Not exclusive to Continental tubes. Rubber does degrade over time and as mentioned, rolling a tube tight to fit into a saddle bag for extended periods can make the valve area more susceptible to cracking. It's unfortunate but can happen to any tube if not optimally stored.