I had the same problemn. It happended with old and slow pc´s and the conclusion was that it was the rendering, just as it was said in this thread.
The only thing to do was to use
SET ENGINEBEHAVIOR TO 80 when it was and old pc with W98 and use
SET ENGINEBEHAVIOR TO 90 with WXP, any pc with WXP it's supposed to be fast enough to deal with that rendering issue.
I´m not using the Report´s dataenvironment, the cursors are already opened in the form.
Hernan