An upgrade of Drupal core from 7.10 to 7.12 causes secondary menu blocks to disappear, in spite of the settings in the block interface. I used drush up to perform the upgrade. However, the menu block did not disappear until running drush cc all.
This issue came up with a Main menu (levels 2-4) block assigned to Sidebar First in the Omega theme framework. Changing the top level of the menu to 1st level primary made the menu re-appear, as did re-assigning the block to another random menu, such as Navigation or Development.
I tried creating another menu block with the same settings, and experienced the same issue.
I was able to restore visibility by rolling back upgrades to core and contrib modules. By adding them back one by one and running drush cc all between upgrades, I was able to establish that it was indeed the upgrade to Drupal core that caused the bug.
An image of the menu block settings is attached.
|'Main menu (levels 2-4)' block.png||288.87 KB|