I was unable to recreate the same scenario as in the description. No matter how tags are inserted in the Editor the self-closing ones stay always the same.
Please provide more details what are the steps leading to the encountered behavior. On a side note, provide more details about the configuration of the RadEditor and especially the enabled/disabled content filters.
Check out the Telerik Platform - the only platform that combines a rich set of UI tools with powerful cloud services to develop web, hybrid and native mobile apps.