protobuf.js version: v6.6.4

When deserializing sfixed64 values, the Long object returned contains data that is smaller by a factor of 2.
I've compared v5.0.2 results with v6.6.4.

• Identical base 64 input
• output of Long values is different by a factor of 2

v6.6.4

const pbEntity = pbRoot.lookup(schema);
const buffer = Buffer.from(base64Data, 'base64');
const entity = pbEntity.decode(buffer).toObject({ bytes: String, enums: String, arrays: true });

v5.0.2

const entity = protoBufBuilder.build(schema).decode(base64Data).toRaw(true);

When I removed the zzDecode call, I got correct results:

function read_sfixed64_long() {
    return readFixed64.call(this).toLong();
}

instead of:

function read_sfixed64_long() {
    return readFixed64.call(this).zzDecode().toLong();
}

I think that the implementation might need to be identical to fixed64.
If needed, I can write some code to repro the problem in isolation.