Table in a Table - with two DataSet - bad output

jati

Hi everybody!

I'm quite new to BIRT. I would like to create a master-detail report which uses two dataset but there is an outer join between them. The two dataset can be connected on two fields, so JointDataSet seems not to be the proper way.
The report works fine, but the print output looks funny because the outer dataset has 75 rows result and the inner set has only 6 rows.
I reduced the padding (top, bottom) to zero in the inner table, but the HTML output shows (i guess) the outer rows which doesn't have child records. The PDF output makes a page break after four lines.
I don't know what to do to get the correct output.
The attached outputs have many colors because I was able to find the parent of the spaces only this way.

Any help would be appreciated!