Hello, here is what I noticed trying to play with multiWidgetEditor :

1. open the workbench and ensure the multiwidgeteditor is opened as well
2. close the editor (the grey emplacement where the editor used to be is still here, waiting for a new editor to come)
3. now try to move this container and to dock it inside itself (either on the bottom, left, right or top)

-> The container is duplicated and both container can't be deleted, when a new editor is opened, there is still one empty container remaining (this can be repeated as much as you want)

One way to overcome this issue is to forbid the creation of a new PartStack when droping an empty list of part pane onto it in berryPartSashContainer.cpp (see attached diff)

I don't know how far it goes against the original wanted behavior, nor what would be the side effects of this, but for now it seems to work