This issue affects both the Login module as well as the Logout menu item redirects.
I have tested this on development and a vanilla installation of Joomla 3.6.0 stable with same results with sites using varying versions of PHP5.6 and 7.

Steps to reproduce the issue

1. Create a logout menu item.
2. For the Logout menu item set a redirect page.
3. In the Login module, set a login and logout redirect page.
4. Login to the website and see if you are redirected to the proper page.
5. Now logout of the site using the Login module's logout button.
6. Login again and then logout using the Logout menu link you previously created.

Expected result

Login and logout should redirect to the proper pages.

Actual result

Logout button in the logout module and the Logout menu item is not redirecting to the assigned pages.
The URL shows a non-SEF URL when logging out via both methods even if SEF URLs are enabled.
Example of URL shown when logging out is:
http://mysite.com/index.php?option=com_users&task=user.logout&8bbd8228ca6184b4718b255cb797e75a=1&return=aW5kZXgucGhwP0l0ZW1pZD0xMDE=

System information (as much as possible)

1. Tested in both PHP 5.6 and 7.0.2
2. SEF URL's are enabled. Tested with and without mod_rewrite enabled with same results.
3. Tested in development sites on localhost server as well as live hosting servers at Cloudaccess with same results in all environments.
4. Tested in a vanilla 3.6.0 Stable installation as well as multiple dev sites and one live site.