Hiding all blocks on one side of a course page makes the entire region hidden, even with editing on. This means the hidden blocks on that side can not be accessed to unhide them.

Steps to reproduce:

1. Open a course with blocks on both sides.
2. Make sure no blocks are docked.
3. Turn editing on.
4. Make each block on the right hidden.

Notice that the entire right column is now gone, with no way to view or unhide the hidden blocks.

Workarounds:

1. Dock one of the visible blocks on the left to make the right column re-appear.
2. Make at least one block on the right visible.

We're using a custom Clean-based theme, running Moodle 2.7.2+ (Build: 20141028). The issue can be reproduced with the Clean theme on demo.moodle.net (Moodle 2.8.1 (Build: 20141113).