I've just installed Kibana 6.2.2 on Ubuntu, along with the XPack plugin to secure my install.
I'm experiencing a weird problem where if I log in as "User A", I show as being the "kibana" user along with that user's security privileges. This occurs even if I clear out my cookies and browser local storage.
If I open an incognito window, it works fine. I show as User A. No problems with Safari or Firefox either.