only creating single session per user

I guess my first question is, under what circumstances will another session be created?
I am signing in using a different tab, but I'm on the same device. Only one session is being created, here's the current flow of what I'm observing:
Sign in on Tab 1 > Session created
Sign in on Tab 2 > Session (from Tab 1) removed > New session created

I'm not signing out of Tab 1, so the session created for it shouldn't be removed. I am sure the session is being removed because the new session gets a different id and I'm no longer seeing Tab 1 session's id.
Was this page helpful?