1. Open a panel in admin mode
2. Open "Add content" dialog on a pane
3. Select "New custom content". Window with CKEditor loaded appears:
4. Close the window using either "Close window" control or by pressing "Cancel" button.
5. Repeat adding custom content. Now the window lacks CKEditor:
and error message appears in js console:
I use jQuery 1.8 provided by latest jQuery Update dev