I have a Report with subreports. In one of the subreports is a group around a subreport with the property "Keep together" switched on. In this subreport is in the summary band a crosstab.
If there is not enough space for the columns of the crosstab on one page, then JR put an empty page before the Group and then breaks the crosstab. If the property is switched of, then it works fine.
I think there should not be an empty page before the group when the property is switched on.