Cookie / cache issue?

I am not using any caching plugin (and there is none on the server) and I am experiencing the following behavior.

Member wants to view protected content > goes to login page, logs in successfully, page is redirected to home page. If the user then goes back to the page that is protected, they still see the login message. At this point if you force refresh (CRTL+f5) the hidden content appears.

I can;t find any explanation for why you would need to force refresh as if you are trying to clear cache to see the content – can you help?