<!-- This issue tracker is only for technical issues related to Bitcoin Core.

General bitcoin questions and/or support requests are best directed to the Bitcoin StackExchange at https://bitcoin.stackexchange.com.

For reporting security issues, please read instructions at https://bitcoincore.org/en/contact/.

If the node is "stuck" during sync or giving "block checksum mismatch" errors, please ensure your hardware is stable by running memtest and observe CPU temperature with a load-test tool such as linpack before creating an issue! -->

<!-- Describe the issue -->

Starting with the following unsigned transaction:

```
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
```

I first call:

```
walletprocesspsbt "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" true ALL true
```

Which generates:

```
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
```

Which is "complete: true" and parses fine. But then if I run `walletprocesspsbt` on the result AGAIN (don't ask why ... or do, but this should be idempotent):

```
walletprocesspsbt "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" true ALL true
```

I get the following:

```
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
```

Which is still reported as "complete: true", but when I try to decode or finalize it:

```TX decode failed PSBT is not sane.: unspecified iostream_category error (code -22)```

I would expect `walletprocesspsbt [foo] true ALL true` to be idempotent, or at least produce output that's parseable.

This is all testnet and I have attached the wallet.dat in case it's useful (it only has two UTXOs and very few keys.).

I am going to continue trying to debug this, but I figured since I haven't gotten it yet I should document it. Please let me know if someone else starts looking into it.

{ "wallet",             "listreceivedbylabel",              &listreceivedbylabel,           {"minconf","include_empty","include_watchonly"} },
    { "wallet",             "listsinceblock",                   &listsinceblock,                {"blockhash","target_confirmations","include_watchonly","include_removed"} },
    { "wallet",             "listtransactions",                 &listtransactions,              {"dummy","count","skip","include_watchonly"} },
    { "wallet",             "listunspent",                      &listunspent,                   {"minconf","maxconf","addresses","include_unsafe","query_options"} },
    { "wallet",             "listwalletdir",                    &listwalletdir,                 {} },
    { "wallet",             "listwallets",                      &listwallets,                   {} },
    { "wallet",             "loadwallet",                       &loadwallet,                    {"filename"} },
    { "wallet",             "lockunspent",                      &lockunspent,                   {"unlock","transactions"} },
    { "wallet",             "removeprunedfunds",                &removeprunedfunds,             {"txid"} },
    { "wallet",             "rescanblockchain",                 &rescanblockchain,              {"start_height", "stop_height"} },
    { "wallet",             "sendmany",                         &sendmany,                      {"dummy","amounts","minconf","comment","subtractfeefrom","replaceable","conf_target","estimate_mode"} },
    { "wallet",             "sendtoaddress",                    &sendtoaddress,                 {"address","amount","comment","comment_to","subtractfeefromamount","replaceable","conf_target","estimate_mode"} },
    { "wallet",             "sethdseed",                        &sethdseed,                     {"newkeypool","seed"} },
    { "wallet",             "setlabel",                         &setlabel,                      {"address","label"} },
    { "wallet",             "settxfee",                         &settxfee,                      {"amount"} },
    { "wallet",             "signmessage",                      &signmessage,                   {"address","message"} },
    { "wallet",             "signrawtransactionwithwallet",     &signrawtransactionwithwallet,  {"hexstring","prevtxs","sighashtype"} },
    { "wallet",             "unloadwallet",                     &unloadwallet,                  {"wallet_name"} },
    { "wallet",             "walletcreatefundedpsbt",           &walletcreatefundedpsbt,        {"inputs","outputs","locktime","options","bip32derivs"} },
    { "wallet",             "walletlock",                       &walletlock,                    {} },
    { "wallet",             "walletpassphrase",                 &walletpassphrase,              {"passphrase","timeout"} },
    { "wallet",             "walletpassphrasechange",           &walletpassphrasechange,        {"oldpassphrase","newpassphrase"} },
    { "wallet",             "walletprocesspsbt",                &walletprocesspsbt,             {"psbt","sign","sighashtype","bip32derivs"} },
};
void RegisterWalletRPCCommands(CRPCTable &t)
{
    for (unsigned int vcidx = 0; vcidx < ARRAYLEN(commands); vcidx++)
        t.appendCommand(commands[vcidx].name, &commands[vcidx]);
}