With no images or better descriptions I don't see how we can tell you what EXACTLY happened. I have seen more than a few Schreader valve stems, that are the common rubber/molded in type, develop a blister from the inner metal separating from the surrounding molded rubber "jacket". This blister can open (blow out), or not (and that's a funny thing to see, a goiter on one's valve side
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As to what might cause this I can only think of two reasons. One is a faulty stem molding, not unheard of but fairly uncommon and far less to be repeated by the next tube. The other is bad valve use. If the valve stem is wagged or pulled a bunch its internal bonding to the rest of the tube can be damaged. Others might have more experience or understandings. Andy