Sec1 round-trip fails with AlgorithmParametersMissing

While testing with rustls I noticed that sec1-der and pem exported ec private keys would fail to decode. The following is a minimal reproducer. I will say, this could be my fault for mishandling the API somehow, but after a lot of testing and verification I think there may be a fault in the way that sec1 is encoded.

Any advice would be welcome.

#[cfg(test)]
mod tests {
    use p384::ecdsa::SigningKey;
    use p384::pkcs8::DecodePrivateKey;
    use p384::pkcs8::EncodePrivateKey;
    use p384::SecretKey;
    use sec1::DecodeEcPrivateKey;

    #[test]
    fn sec1_pem() {
        let mut rng = rand::thread_rng();

        let signing_key = SigningKey::random(&mut rng);

        let server_private_key_pem = SecretKey::from(&signing_key)
            .to_sec1_pem(Default::default())
            .unwrap();

        let _ = SigningKey::from_sec1_pem(server_private_key_pem.as_str()).unwrap();
    }

    #[test]
    fn sec1_der() {
        let mut rng = rand::thread_rng();

        let signing_key = SigningKey::random(&mut rng);

        let server_private_key_pem = SecretKey::from(&signing_key).to_sec1_der().unwrap();

        let _ = SigningKey::from_sec1_der(server_private_key_pem.as_slice()).unwrap();
    }
}

thread 'tests::sec1_pem' panicked at src/lib.rs:19:76:
called `Result::unwrap()` on an `Err` value: Pkcs8(PublicKey(AlgorithmParametersMissing))

thread 'tests::sec1_der' panicked at src/lib.rs:30:78:
called `Result::unwrap()` on an `Err` value: Pkcs8(PublicKey(AlgorithmParametersMissing))

[package]
name = "rustcrypto-sec1"
version = "0.1.0"
edition = "2021"

[dependencies]

p384 = "0.13"
sec1 = "0.7"
rand = "0.8"

Start by running the provided sec1_pem and sec1_der tests in src/lib.rs and reproducing AlgorithmParametersMissing with the listed p384 and sec1 versions. Trace the failure through the SEC1 and PKCS#8 decoding paths. Done means the encoded private key round-trips successfully in both PEM and DER forms, with regression coverage for both cases.