Tx builder ends with the wrong collateral return amount

[mpizenberg]

Describe the bug
Building a mint Tx that ends with a wrong collateral balance, with added native tokens.

The code I’m using to build the mint Tx is the following:

def mint_badge(context, wallet_address: Address, validator, picked_utxo):
    builder = TransactionBuilder(context)
    builder.add_input_address(wallet_address)

    # Get the first wallet UTxOs to guarantee mint unicity
    builder.add_input(picked_utxo)

    # Mint the token
    policy_id = validator["hash"]
    mint = MultiAsset.from_primitive({policy_id: {b"": 1}})
    builder.mint = mint

    # Add the script to the witness set
    script = PlutusV3Script(validator["compiled_code"])
    builder.add_minting_script(script, Redeemer([]))

    # Build the tx
    tx_body = builder.build(change_address=wallet_address, auto_required_signers=False)
    tx_witness_set = builder.build_witness_set(True)
    return Transaction(tx_body, tx_witness_set)

Most of the time this works, but today it generated the following Tx for me (cbor)

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

As you can see in this screenshot from Eternl detailed Tx view, the collateral output contains more native tokens than the input being consumed

As a result, ogmios gave me the following error message.

ogmios.errors.ResponseError: Ogmios responded with error: {'jsonrpc': '2.0', 'method': 'submitTransaction', 'error': {'code': 3133, 'message': "One of the input provided as collateral carries something else than Ada tokens. Only Ada can be used as collateral. Since the Babbage era, you also have the option to set a 'collateral return' or 'collateral change' output in order to send the surplus non-Ada tokens to it. Regardless, the field 'data.unsuitableCollateralValue' indicates the actual collateral value found by the ledger", 'data': {'unsuitableCollateralValue': {'ada': {'lovelace': 2896254}, '53c94b1a4a7a79eb71c45a17ddcb65207eea77fba087d43fccbd4035': {'': 1}, '9295b9e76efeb135a2d53b69f6bd907af9eef753f273596e0d319233': {'': 1}}}}, 'id': None}

I’m using pycardano 0.13.2 on Macos.

[mpizenberg]

It seems the builder selected the same utxo for the input and for the collateral in this case (which is possible). However, the collateral output appears to have double the amount of native tokens