Steps to reproduce

1. Switch to the classic theme.
2. Create a course and add a module.
3. In the Navigation block, expand the section where the module has been created.
4. Delete the module.

Expected behaviour

The module is not displayed on the page.

Current behaviour

The module is not displayed in the main course content region but it still appears in the Navigation block.

It can also be reproduced in boost (the problem seems to be in the Navigation block).