Clear Umbraco IsDirty flag after editing in custom backend tab

I can't stop Umbraco asking if I want to save my data when I move off my custom tab in the backend unless I use no-dirty-check attributes.

I've tried creating a to contain my controls, and called $setPristine() and $dirty=false on that, but it's made no difference.

It seems like the umb-dashboard form is the one causing the save changes dialog - but I can't work out how to get a reference to that from the Umbraco services. angularHelper.getCurrentForm() always returns null.