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I now superglue the valves in before using them. I can see that this design is kinder to the valves and potentially more serviceable but incredibly infuriating at the time, especially if in the field. I got a valve cap with integrated valve spanner on to ensure I always have a way to try and nip them up along with superglue now in my puncture repair kit (also useful for tyre cuts).
Fibreglass
Yes. No matter how tight they're done up. The pumps also like to unscrew themself. And I've had a core snap in the tube too.