Steps:
1) Go to /admin/structure/blocks
2) Use the 'Place Block' function next to a region, for example the 'Sidebar Second'.
3) Choose 'add custom block'
4) On the 'Configure Block'-page the region you've selected on step #2 is not selected.
I know this ain't a huge bug, bit I teach a lot of people who haven't used Drupal before, and most people experience this behavior as a bug. (aka. it doesn't responds as expected).
Thanks for your time!
Keep up the great work.