Witness scheduling isn't based on IRB, only the extent that a witness will roll back is. Therefore, it is possible for votes cast in the pending state to impact the pending witness schedule and ultimately advance the LIB.

Can you please review this algorithm for me: https://github.com/tendermint/tendermint/wiki/Byzantine-Consensus-Algorithm

Under the model used by tendermint, no block can contain data that changes who can confirm it.