go: Horizon returned bad sequence error although the transaction was added to ledger

What version are you using?

I am working on the public network through the public Horizon instance: https://horizon.stellar.org. I posted transactions to the network using this API: https://www.stellar.org/developers/horizon/reference/endpoints/transactions-create.html.

What did you do?

On may 8, I started posting a transaction on 06:47:19 UTC. 30 seconds later, on 06:47:49, a https://www.stellar.org/developers/horizon/reference/errors/timeout.html was returned. As instructed in the documentation, I retried sending the same transaction after a second delay. Within less than a second I got a bad sequence failure:

{
 "type": "https://stellar.org/horizon-errors/transaction_failed",
 "title": "Transaction Failed",
 "status": 400,
 "detail": "The transaction failed when submitted to the stellar network. The `extras.result_codes` field on this response contains further details. Descriptions of each code can be found at: https://www.stellar.org/developers/guides/concepts/list-of-operations.html",
 "extras": {
 "envelope_xdr": "AAAAAGRFCbG4m7/GKYJDKVwWrhSAhfgjSjOILbb0cOAN+rH+AAAAZAGfEqQAAC2bAAAAAQAAAABetP9IAAAAAF61DoQAAAABAAAAG1hMTSBlMmUgbW9uaXRvciB0cmFuc2FjdGlvbgAAAAABAAAAAAAAAAEAAAAA+dkdOXuuwsV5OpRuUk9Owqe6ocz1ukhgrYqnKliCQA8AAAAAAAAAAAAAAAEAAAAAAAAAAQ36sf4AAABAhnftLR7Lx9hKXojyGkKDLu4bdI4+wgx/qSPxEW3Vr9CAWBDQPngRWihDppCNzpmKTn3Q3wsM0z3qOJl6+72zCA==",
 "result_codes": {
 "transaction": "tx_bad_seq"
 },
 "result_xdr": "AAAAAAAAAAD////7AAAAAA=="
 }
}

My code treated this as failure. However, I was surprised to find the transaction on the chain: https://stellar.expert/explorer/public/tx/45a9674370754d50b50df23e03d7fa87bd6ee70bd2db2431a8ab874218c3115a.

What did you expect to see?

I expected to see a successful submit result, either on the first attempt which ended in timeout or on the second attempt which ended in tx_bad_seq.

What did you see instead?

I got a wrong misleading tx_bad_seq failure.