I came across a problem with a panels page when I check the "Disable Drupal blocks/regions" box, the sidebars are supposed to disappear so that the content takes the full width. But it didn't work.

Switching back to Garland and the sidebars disappeared as expected. After a quick search, I found this post on drupal.org which is the same issue but one of the replies essentially says to hack core to get it to work, but that is not necessary.