Are you creating the page from within an area's Create link, or are you using the navbar/index Create link and selecting an area later?
It is possible that the navbar/index route does not delete the draft. I have not tried that. There is not a XenForo example of this kind of scenario to draw on for consistency, but the behavior might still feel incorrect in some cases. On a technical note, if this is not working, perhaps we would need to explicitly pass the draft container if a draft is used, since I think that information can get lost once you choose a different area in the picker.