Since last few months i m seeing the same results. Like when i m logging into my analytics account using a gmail account and after checking stats for that day , i normally logout from analytics account. After that whenever i browse youtube, gmail, or google i m already logged in. This is a tricky part google started playing.
To be safe whenever i logout from analytics account i normally visit youtube,gmail and google and signout from my account.
P.s: I don't have any google softwares installed on my computer.