You may have noticed that IE 11 in ‘Document Mode: Edge’ (developer's tools, F12 > Emmulation > Mode > Document Mode) will always prompt for re-login when the site’s session times out or the user clicks logout (6.9 or earlier).
Other browsers, or versions of IF, do not require the retyping of the credentials and used the cached ones instead allowing direct access to the sites.
This is a product defect (TF00625249). It’s a compatibility issue with ‘Document Mode’: Edge.
Set IE 11's ‘Document Mode’ default setting to something other than ‘Edge’.
The behavior is not observed on the latest version of the product: 7.0.2