test that showcases panic when PubKeyMultisigThreshold are used in sdk:

- deserialization will fail in `readInfo` which tries to read a
 `crypto.PubKey` into a `localInfo` (called by
  cosmos-sdk/client/keys.GetKeyInfo)

crypto/multisig/threshold_pubkey_test.go

@@ -95,6 +95,22 @@ func TestMultiSigPubKeyEquality(t *testing.T) {
 	require.False(t, multisigKey.Equals(multisigKey2))
 }
 
+func TestPubKeyMultisigThresholdAminoToIface(t *testing.T) {
+	msg := []byte{1, 2, 3, 4}
+	pubkeys, _ := generatePubKeysAndSignatures(5, msg)
+	multisigKey := NewPubKeyMultisigThreshold(2, pubkeys)
+
+	ab, err := cdc.MarshalBinaryLengthPrefixed(multisigKey)
+	require.NoError(t, err)
+	// like other crypto.Pubkey implementations (e.g. ed25519.PubKeyEd25519),
+	// PubKeyMultisigThreshold should be deserializable into a crypto.PubKey:
+	var pubKey crypto.PubKey
+	err = cdc.UnmarshalBinaryLengthPrefixed(ab, &pubKey)
+	require.NoError(t, err)
+
+	require.Equal(t, multisigKey, pubKey)
+}
+
 func generatePubKeysAndSignatures(n int, msg []byte) (pubkeys []crypto.PubKey, signatures [][]byte) {
 	pubkeys = make([]crypto.PubKey, n)
 	signatures = make([][]byte, n)