Anyone ever see this before?

A user logs in, opens an item in a module that only allows authenticated users.  User copies the URL of that item.  Then logs off.  Closes all windows... then opens a new browser, logs in and pastes the copied URL into the browser and hits enter.  DNN then shows the user as being logged out instantly.  But if the user clicks on log-in....  DNN shows them as being logged in.  They don't need to enter a user name or password.

Or..  log-in, open a thread... copy the url and log out.  then paste that url into the URL of the browser and hit enter.  DNN automatically shows you as logged in.  But...you logged out.

Is this just an issue with DNN 4.x?

I agree, Local caching will cause this behavior.  I bet the page is showing up very quickly when you go back, and then when you refresh it will take a while to load.