When this happened to me it was down to an old tyre which started to move in the rim, e.g. when braking, and it was not until I saw that the plastic rim tape was scrunched up on one side of the valve by the movement of the tube against it that I realised what was happening.
It’s not the tyre moving on the rim, it’s the action of the circumference of the tyre when the tyre gets deformed during rotation.
If so, then there is more than one potential cause of these types of punctures at the valve stem, which is frustrating because it is potentially going to make it harder to diagnose the problem. That said, I am somewhat sceptical: all tyres on all bikes will deform during rotation, and even allowing for variation in tyres, tubes, rims, pressures etc., I would have expected a lot more punctures to be reported and ascribed by people generally down to this if it was a significant cause.
My suggestions would be:
– double and triple check the tyres and tubes (they are the correct sizes for each other and for the rim, and the bead is in good condition?)
– I would instinctively tend to use a highish pressure.
– I prefer inner tubes with threaded valves. This does not cure the underlying problem, but the locknut will stop small movements of the valve stem and keep it at 90 degrees to the rim. Possibly more importantly, I found that the cheap chinese inner tubes where the butyl extended up the valve stem were prone to puncturing as a result of the rubber around the stem being cut or abraded by the edge of the valve hole in the rim in the event of even very slight tube movement.
With regard to using talc to reduce the extent to which the tube moves with the tyre, I suspect that whilst this may help, there is still an underlying cause at work which needs to be identified, and talc (and similarly a threaded valve stem) only masks the underlying cause and/or delays the puncture.