I've been tearing my hair out over this for a couple of days, so hopefully someone can help point me in the right direction.
I recently inherited this site from another developer, so I'm not super-familiar with its idiosyncrasies. It appears to be a custom theme. It's probably built off of Twenty Eleven or something, but I can't say for sure. It has about 50 plugins installed.
One section of the site (which is behind a login, so I can't link you to it, sorry. Check out the image below) displays a "phantom" widget. That is, on each of the pages within that section, the secondary widget area is set to be empty. Despite that, the phantom widget appears.
Here's the widget in question: http://i.imgur.com/Diuhn.png
If I select a widget to appear in the secondary widget area, the phantom widget is replaced with whatever I selected. As soon as I make the secondary widget empty again, the phantom widget returns.
Previously Attempted Solutions
As I mentioned, I have checked to make sure the pages don't have any secondary widget selected.
One of the many plugins is called "Custom sidebars," and it seems to completely manage the sidebars. I tried turning it off and all of the sidebars on every page disappeared completely. It could be the culprit, but at this point I'm not sure how to test further.
I checked out the menu and sidebar setups for the section. Neither has the phantom widget, so I'm pretty sure it's not them.
I have checked several template files for the pages within the section. They only make a call to
sidebar.php does not appear to be out of the ordinary. I added a class to the
div in that file where
id="secondary" and saw that change reflected in the phantom widget's containing
div. In side the
div is the WordPress function
dynamic_sidebar( 'secondary-widget-area' );.
I've poked around in various core files without any luck, but I may have missed something. If anyone can point me in a direction, I would be much obliged.