When the newly introduced `"maxfeerate"` option is not passed, the default fee rate is interpreted as an absolute amount. However, when it is passed, it is interpreted as a fee rate. Thus, the rpc will return different results when the value is explicitly set to the default.

See

https://github.com/bitcoin/bitcoin/blob/536590f358dc3d3e5821eba7f1009452ea93b205/src/rpc/rawtransaction.cpp#L797-L807

I think we should change it back to an absolute value in BTC (not a feerate)

This was changed to a feerate by @kallewoof, so ping him to see if there was a specific reason to switch.
"  \"version\" : n,          (numeric) The version\n"
            "  \"locktime\" : ttt,       (numeric) The lock time\n"
            "  \"vin\" : [               (array of json objects)\n"
            "     {\n"
            "       \"txid\": \"id\",    (string) The transaction id\n"
            "       \"vout\": n,         (numeric) The output number\n"
            "       \"scriptSig\": {     (json object) The script\n"
            "         \"asm\": \"asm\",  (string) asm\n"
            "         \"hex\": \"hex\"   (string) hex\n"
            "       },\n"
            "       \"txinwitness\": [\"hex\", ...] (array of string) hex-encoded witness data (if any)\n"
            "       \"sequence\": n     (numeric) The script sequence number\n"
            "     }\n"
            "     ,...\n"
            "  ],\n"
            "  \"vout\" : [             (array of json objects)\n"
            "     {\n"
            "       \"value\" : x.xxx,            (numeric) The value in " + CURRENCY_UNIT + "\n"
            "       \"n\" : n,                    (numeric) index\n"
            "       \"scriptPubKey\" : {          (json object)\n"
            "         \"asm\" : \"asm\",          (string) the asm\n"
            "         \"hex\" : \"hex\",          (string) the hex\n"
            "         \"reqSigs\" : n,            (numeric) The required sigs\n"
            "         \"type\" : \"pubkeyhash\",  (string) The type, eg 'pubkeyhash'\n"
            "         \"addresses\" : [           (json array of string)\n"
            "           \"12tvKAXCxZjSmdNbao16dKXC8tRWfcF5oc\"   (string) bitcoin address\n"
            "           ,...\n"
            "         ]\n"
            "       }\n"
            "     }\n"