exception inheritance in web service

[Yan Zhou]

When it comes service-specific exception, Sun's Web Service Blue Print early access says:
Exception inheritance is lost when service end point throws a service specific exception. For instance, if I have ServiceException derived from RootException, which dervies from Exception, and the code throws ServiceException, the documentation seems to indicate that the data and methods derived from RootException will be lost when the exception reaches the client.
I am not sure I understand this, could anyone explain why this is so?
Thanks.
Yan