Hi Chee Boon;
Yes, this has been a handicap of the CrossTab DW in PB for quite some time. My suggestion would be to open a support ticket on this issue. Opening up a ticket is important as it will be officially recorded and after an internal review of the DW code as a bug, may then get placed on the official enhancement list if not immediately fixable.
Regards ... Chris Pollach
Appeon: Director, Developer Relations.