Signer reports the miner block proposal pubkey does not match the winning pubkey hash for its sortition

[obycode]

There seems to be a bug somewhere that exposes itself as a signer considering a proposal invalid, printing the warning "Miner block proposal pubkey does not match the winning pubkey hash for its sortition. Considering invalid." (from stacks-signer/src/chainstate.rs:301).

This issue has been detected twice on mainnet. Both times, it happened after a quick Bitcoin block triggered a potential reorg of the prior tenure. The signer in question approves multiple blocks in the new, reorging tenure, but then rejects a proposal with this warning. Other signers accepted the same proposal with no trouble. When the miner proposed another block, this signer accepted it.