Maybe you have the safety setting "Validate Derivations" disabled that enabled you to use the single-sig derivation paths to MultiSig.
No, it is on. BIP 49 is a multisig derivation path though.
I have no means to test this but you may be able to sign by creating a new MultiSig wallet with the correct derivation paths to the provided extended public keys.
I think you're right. The $30 locked in that wallet is the cost of tuition.