Hi Stuart Hemming,
In fact this is the expected behavior. When a column (or table) is renamed in the database we cannot really be sure that this has happened, the database gives no information about such changes. However, by comparing the schema before and after we see that one of the old columns is missing and new one has been added. The default action we would perform in this case is add a property to map the new column. The old property will not be deleted in order to preserve the changes you might have done there, but it will be left unmapped. You can see that the old property is not associated with a column in the Mapping Details Editor.
If you would like to use the old property with the renamed column you can use the Details Editor to unmap the newly generated property and map the column to the old one. You can then remove the new property (just delete it from the diagram) and rename the old one if needed.
There is also another way to update the model when something has been renamed in the database. If you have not already run the Update From Database wizard, open it and follow the instructions in this article
, under the Modify section. This way you will be able to merge the Add and Remove actions into a single Modify action and update the old column instead of adding new one.
Hope that helps.
All the best,
the Telerik team