Subdoc multi-part lookup failing on centos

When testing against a recent server build (5.0.0-3088), we're seeing a particular subdoc operation succeed when running on osx, and fail when running on centos 7.

The subdoc operation is a multi-part lookup that attempts to retrieve a system xattr and the full document body.

It's returning 0xCC (PROTOCOL_BINARY_RESPONSE_SUBDOC_MULTI_PATH_FAILURE) when running on centos 7, but succeeding when running on osx.

Our steps to repro are just:
1. Create a doc w/ a system xattr
2. Attempt to retrieve that doc with a multi-op subdoc Lookup – the first op requesting the xattr, and the second requesting the full doc.

This appears to be failing for all docs w/ system xattrs (doesn't seem to depend on the doc contents).

This operation was working in earlier Spock builds - at minimum this worked for the Spock beta.