If a Date object is created in Javascript (new Date()), and is serialized with MessagePack, then PHP will fail to deserialize with the following message:
PHP Warning: [msgpack] (php_msgpack_unserialize) Parse error
This happens if the Date object is by itself, or part of another object. It also happens if the serialization is done with either of the two javascript libraries listed on https://msgpack.org
MessagePack Specification: https://github.com/msgpack/msgpack/blob/master/spec.md
Expected Behavior: Javascript Date is deserialized to PHP DateTime.