Here's another approach:
This assumes that you have two columns, with format in multiple columns checked, and in the layout section, format groups with columns is checked. As SV noted, the repeat group headers on each page should be turned on.
First, insert a second details section_b. In design mode, magnify the view so that you can ensure that the group header and the two detail sections are exactly the same size. Suppress the report header (or start a new page after), and suppress the group footer, if you're not using it.
Create two formulas:
//@reset} to be placed in the page header:
whileprintingrecords;
numbervar linecnt := 0;
//{@linecount}:
whileprintingrecords;
numbervar linecnt := linecnt + 1;
Place this last formula in the Group Header, Detail_a, and Detail_b. Place the fields you want to display in the detail_a section. In the detail_b section, copy the GroupName that is already displayed in the Group Header.
Next note the number of records you are getting in the first column of each page and also note the last number on the page. In this example, there are 58 records in column 1 and a total of 115 on the page.
Then go to the section expert (format->section)->detail_b->suppress->x+2 and enter:
remainder({@linecnt},58) <> 0 or
previous({table.groupfield}) <> next({table.groupfield})
Then still highlighting detail_b, go to "New Page After"->x+2 and enter:
not onlastrecord and
remainder({@linecnt},115) = 0
-LB