In reply to Mike.

At least on Oct 7th 2016, Beta 15 of the plugin was updated to include support for Post Meta, etc. However, it's not automatic and requires a register_meta() call.

Third party protected meta can that was prefixed with an underscore and can be unprotected to be registered but isn't straightforward as it could be perhaps.

For my many of my own custom fields, I often choose not to prefix them. Instead, I use the is_protected_meta() filter as it eliminates many issues I've learned.