Updated the editor code to write to the CRM field every time a change is made to the HTML, rather than waiting for the 'blur' event, which doesn't fire when closing the form directly from the editor when auto save is enabled.
Known issue in CRM 2016 v8.2.0 where the field value is still not saved in the above scenario - This issue is resolved in Service Update 1 for v8.2.2 - "AutoSave is not working when navigating to the home button."