BIP125 rules 3 and 4 are not being checked properly according to my understanding:

https://github.com/bitcoindevkit/bdk/blob/c2b2da7601fb570952cfd858f3821b3a4fd87ec9/src/wallet/mod.rs#L730-L746

It should be checking rules 3 and 4 regardless of the fee policy chosen in txbuilder.