Let me get this straight - you run a report and there is a button or link in the heading (not the body) of the report that will run another report.
A couple of possibilities come to mind
1. The button/link is associated with javascript to open a new window and run a report in which case you need to change the target to "_self"
2. The button/link is an href to another report and the target needs to be set to "_self"
3. The stylesheet for the report that you ran has FOCEXEC=something and TARGET='_self' needs to be added to the same item.
for example, the following will always open a new window for the drill down.
TABLE FILE CAR
"This is my country: <COUNTRY"
SUM SALES
BY COUNTRY
ON TABLE SET STYLE *
TYPE=HEADING, OBJECT=FIELD, ITEM=1, FOCEXEC=MYFEX, TARGET='_blank',$
END
Changing TARGET='_blank' to 'myfex' will open a new window called 'myfex' and will be reusable and changing it to '_self' will reuse the same window that the report was origionaly in.