This seems to be happening in both editors and in different scenarios:
  1. When we use the html editor (in the old editor) and create an html element and set id on it e.g. <h1 id=test>Test</h1> then close the editor and reopen it, the html element will be changed to <h1 id=test-1>Test</h1>
  2. When you publish an article using the new editor, all custom HTML id tags are removed. This also happens when we switch from the Source code to the text editor. It seems this feature is not supported in the new editor.
  3. Index numbers are automatically added to the TOC link ID's. The indexnumbers change when you add or remove TOC items completely messes up all external referrals to the chapter.