When a user logs in, and they have checked "Keep me logged in", and they have a global user, the centralauth_Token cookie is only set for the wiki where they are logging in. It is not set for loginwiki, or any of the other SUL wikis.
So the user will be logged out of all the other SUL wikis except the one where they logged in, if they close their browser and then return.
I think we should also set it on loginwiki, so that they will be logged in centrally for 30 days. Other attached wikis can rely on the login check to log them in.