When you edit a multipart transclusion in the VisualEditor TemplateDialog and delete all parts using the sidebar controls, you will end up with a placeholder page to search and add a new template. All fine with that. The controls in the sidebar behave a bit inconsistent in that situation though:

The buttons to move parts up and down are disabled and greyed out.
The button to delete a part is hidden.

We might want to change that behavior to be more consistent. Also hiding that delete button is implemented in a way that feels a bit odd and could be cleaned-up.