Cannot re-submit fully-signed tx if first submission failed

[andywer]

Scenario: All required signatures have been added to the transaction, transaction has been submitted to the Stellar network, but submission failed (because of network congestion / fees or whatever).

Expected outcome

Can re-submit the fully-signed SEP-7 bundle.

What happens instead

400 Bad Request

{
    "message": "Transaction is already sufficiently signed."
}

How to reproduce

POST https://multisig.satoshipay.io/submit

web+stellar:tx?network_passphrase=Public%20Global%20Stellar%20Network%20%3B%20September%202015&xdr=AAAAAMGkzSBnP9lXuRIcYM%2Bk4%2Ffbv%2FRaMX9MYdlko4MpM6jZAAAAZAFOFksAAAAKAAAAAAAAAAAAAAABAAAAAAAAAAUAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAEAAAAAbBh5971XB0LoZtQeHBdlfeJCnY%2B7OimBlCmkj0C84%2BEAAAABAAAAAAAAAAIpM6jZAAAAQNyh%2FueSoIEdgJjnlVUBdNKCk6a%2BPfAgCdVcHfuU9S1fceG2AtMUHsvbLDquaLRek2y73GvVq1dJoTpNMgqVhA29RxNxAAAAQB25llfeLKiUujEhDsScfx%2F9wJD6w70ireNqGgs0MxJIEKk3LSh%2FMWatab%2BXyN1ZufnNhyO5ZRIUOtYlOZMBEA0%3D&callback=url%3Ahttps%3A%2F%2Fmultisig.satoshipay.io%2Fsignatures%2Fcollate%2Fef035f20a513194cbba7cd9bc683f672da7f68c6da69f9ceb895ee642bb7d1b4