Report line spacing issue

There is a formatting issue that I have come across.
The report has three groups and these groups have headers. When the report is populated most of the time it prints the result properly as expected, but sometimes at different number result records of the query I see that the main group header consumes an entire page and then skips to the next page. But in the next page I get the main group header and the data as it should be printed. After adjusting a page header (not the group headers) the report behaved normally for the same set of data, but fails when the result is changed again.
Any idea what I have done wrong or need to set (maybe a line size or something ) ?Often times when I have that problem, it's due to the "Keep Group Together" option.

Right click on the group name, and choose, "Change Group." Uncheck the "Keep Group Together" box, if it's checked. That might not be the same issue, but it usually resolves the problem with me.

Good luck!|||There is no 'Keep Group Together' checked in this case. I had it earlier and removed it also thinking that may be the issue.
The problem mainly is even if I tweek it a bit and get it to work with one set of data if fails for another one later.
Thanks very much for looking at the issue.|||So all your group expert 'keep group together' and your section expert 'keep together' for groups are unchecked?|||I am terribly sorry. I was all this time unticking the 'Kepp Group Together' check box in the 'Selection Expert' window when RMB and select the 'format..' option.
As I unchecked the check box in the 'Change Group Options' window it worked.
Thank you very much for the help.
By the way do you know why is there two options of 'Keep Group Together' in these two windows ?|||The one in the section expert keeps the section together, e.g. your group header has 3 sections and this keeps these 3 sections together.
The one in the group expert tries to keep the whole group together, i.e. the entire group header, footer, details inbetween etc.