Please check this forum posting: https://forum.open-xchange.com/showthread.php?7564-Detailed-User-Data-uid-Field-gt-Software-or-Documentation-Bug
user?action=get returns a field uid which is not yet described at the HTTP API. That field has been added with CalDAV support.
Steps to Reproduce:
Added "uid" field at http://oxpedia.org/wiki/index.php?title=HTTP_API#DetailedContactData.
Released with: 7.0.1-Rev 4