Hi Chris ,
You have gotten it right that in horizontal inheritance the superclasses are not persisted into the database. They should be abstract, but it's not required. If you want each class to be persisted into it's own table you should use vertical inheritance. You can read more about the inheritance strategies here.
Unfortunately the behavior you are experiencing when you add a property to a superclass and nothing is reflected to its descendants is actually a bug. It is already fixed but it will be released with our next service pack.
If you need further information or more detailed explanation don't hesitate to contact us.
All the best and have a nice day,
the Telerik team
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