people who create Ideas in the Ideas Portal are not being automatically assigned as watchers of those ideas and therefore not receiving email notifications when comments are added or statuses are updated.
People who create ideas via the ideas portal are added as subscribers, rather than watchers. Subscribers will be notified when:
An admin response is posted
An Aha! user publicly comments
A portal user comments
An idea status changes (as long as the status is marked as Show in portal, as you noted)
Perhaps you want the users to be added as watchers for a specific reason/workflow? If so, please reach out to us at support@aha.io and we'd be happy to help with that.