I guess you have heard of a removable valve core, but what about an entire stem?
I recently added another abandoned bike to the workshop and while tending to the flat tire I noticed the inner tube held air, but that the valve stem came out of the inner tube if fiddled with (with an explosive release of tyre pressure too!).
While I assume this is a fault in the inner tube, on closer inspection, it doesn’t look like anything has torn or failed. The inner tube has two rubber joints, the second of which seems to hold the stem base. The upper seems just to hold it straight.
I have replaced the inner tube with a new one from Schwalbe, but can a removable valve stem really be a thing? Never seen this before.