I assume (hope) it was one where the stem is mostly rubber molded around a short brass valve at the end.
If so, it's not unheard of. These are somewhat prone to breakage from things like side stress when pumping, or getting scored by the rim when pushed through.
I've always hated this design and prefer valves that are brass all the way to the tube. However brass is more expensive than rubber, and even half an inch adds up when talking about millions.
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