[AccessD] report sorting problem

I have a grouped report based on the following query:
 
SELECT tblTopics.Title, tblTopics.DateDue, tblPublishersContacts.Contact,
tblPartners.LastName, tblTopics.EstimatedFee,
=IIf(IsNull([LastName]),[EstimatedFee],[EstimatedFee]/2) As SplitFee
FROM tblPartners INNER JOIN (tblPublishersContacts INNER JOIN tblTopics ON
tblPublishersContacts.PublisherContactID = tblTopics.PublisherContactID) ON
tblPartners.PartnerID = tblTopics.PartnerID
WHERE (((tblTopics.DateDue) Is Not Null) AND ((tblTopics.DateSubmitted) Is
Null))
ORDER BY tblTopics.DateDue
UNION SELECT Title, DateDue, Contact, LastName, EstimatedFee, 0
FROM tblScheduledItems
ORDER BY tblTopics.DateDue;
 
The report is grouped on the DateDue field and I use the report's grouping
properties to group by the week. 
 
When I run the query, it sorts by the DateDue values, but the grouped report
loses that sort. The records group properly, I just can't get them to sort
properly within the group. 
 
Any help?
Susan H.