The Group Footer Band has the KeepGroupFooterTogether property. If the property is set to false, then the data can be placed on one page and the footer of a group on another, and data of groups will be separated from its footer:

 

 

 

If the property is set to true, then at least one line of data will be together with the footer of a group:

 

 

 

By default this property is set to true.