Hi
In the backend i have noticed that in the drop-down list for the layout selection:
(Product Form, Category Form, Manufactufacturer Form etc.)
displays also the sublayouts.
This should not happen as a sublayout is just a part of the layout.
If you like you can try to use the component layout form field which automatically fetches the layouts found (including overrides) for a specific view of a component.
http://docs.joomla.org/Componentlayout_form_field_type