1. Create a new content type group.
2. Open the form to create a new content type in the new content type group.
3. Do not create the content type but go back in the browser to the content type list of the new content type group.
4. Refresh the list of content types in the new content type group to verify that is is still empty (because content type form was not submitted).
5. Go the list of content types groups.
6. The new content type group can be selected for deletion. Select it and try deleting it.

Expected result:

Content Type group is deleted.

Actual result:

Error message

Argument '$contentTypeGroup' is invalid: Content Type group contains Content Types

is shown.
 
Background:

Check the database and find a content type placeholder with name

__new__*

in the content type table for the content type from step 2. It appears that this content type draft in inaccessible from the UI.