Why isn't the GROUP BY operator being evaluated remotely?

Areas to examine include:

Operator syntax. Verify that the operator can be evaluated at the remote data source.
Number of rows. Check the estimated number of rows in the GROUP BY operator input and output using Visual Explain. Are these two numbers very close? If the answer is yes, the optimizer considers it more efficient to evaluate this GROUP BY locally. Also, do these two numbers reflect reality? If the answer is no, consider updating the nickname statistics using the SYSPROC.NNSTAT() stored procedure.