Fields Not Showing In Dataset

Hi,

I've a stored procedure which returns different number of fields depending on the input parameter.


create proc spSample (@rtnValue bit)
as
if @rtnValue = 0
begin

select field1, field2 from tablename
end
else
begin

select field1, field2, field3, field4 from tablename
end

Have a report execute this stored procedure, set the parameter value = True. Test the query, it returns all the fields as expected. However, on the fields tab of Dataset it always shows field1, and field2 no matter what; I manually add field3 and field4 under Report Datasets tree and they disappear after each execution. Anyway, I'm able to set the report fields as long as I don't refresh the query.

Is this the bug in SSRS? or am I missing something?

Thanks,

-Ash