Major Description
If during an ajax request a component is scheduled for rendering and that component is the controlling child of an enclosure, it will be replaced by the enclosure for rendering (by the AjaxEnclosureListener). However, as an enclosure is not really the parent of the controlling child in the component hierarchy, it won't let the child render its header.
The problem shows when the child has an ajax behaviour. After handling an ajax request and being refreshed, that ajax behaviour will stop working.