Hi Bitcoin Devs,

I recently noticed a flaw in the Sequence lock implementation with respect to upgradability. It might be the case that this is protected against by some transaction level policy (didn't see any in policy.cpp, but if not, I've put up a blogpost explaining the defect and patching it https://rubin.io/bitcoin/2021/09/03/upgradable-nops-flaw/

I've proposed patching it here https://github.com/bitcoin/bitcoin/pull/22871, it is proper to widely survey the community before patching to ensure no one is depending on the current semantics in any live application lest this tightening of standardness rules engender a confiscatory effect.

Best,

Jeremy