We just built a new SP 2013 farm. For some reason when I access the sites, I see I am sometimes logged in as one of our service accounts (sp_crawl). If I refresh the browser, it switches to my normal AD account. I haven't determined a pattern, it seems rather random. Sometimes it opens as me, other times the crawl account. Sometimes it takes multiple refreshes before it switches. My coworker also saw the crawl account, but even more concerning was she saw my name too.
We are using standard http and Kerberos and have UPS set up and synced.
Edit: I looked in the web app user policy and none of the entries have "Account operates as System" checked.
Pertaining to the duplicate question, I did reset my browser and checked windows credential manager (it has nothing in it). However, my coworker was having the same issue.