DataSourceMappingInterceptor not being called

   I am using DevForce Enterprise 3.3.0.3 and I�m trying to use a r to change various table mapping properties depending on certain conditions.
I have implemented the following DataSourceMappingInterceptor in my Model project:

      public class LegacyDataSourceMappingInterceptor : DataSourceMappingInterceptor
      {
            public LegacyDataSourceMappingInterceptor()
            {
            }
            public override void UpdateSourceMapping(IdeaBlade.Util.IDataSourceKey key, EntityTable entityTable)
            {
                  base.UpdateSourceMapping(key, entityTable);
            }
      }

This assembly is listed in the IdeaBlade.ibconfig in a <probeAssemblyName> element.  However, my UpdateSourceMapping method is never called, nor is the constructor called. 
The documentation is sparse but I believe I am doing everything correctly.  What else do I have to do to get this method called?