Extending DP classes - compiler doesn't recognize datasets

Hi,

While extending the DP classes, it seems the compile does not recognize the datasets, unless atleast one dataset is defined in the extended class.

Example- Extend the ProjInvoiceDP class and try to use the extended class as DP for a report, it throws error. However if datatset methods are implemented again in extended class, the datasets are doubled.

Is it a known issue with extending DP classes.

Thanks in advance