Yes, the Mosaic value is the default one. However the last field will always try to fill up the entire space of the section unless the width is set explicitly. One option is to chnage the CellMaxWidth or Width for the fields in the grid or just for the last one. You migh also achive the desired result with modifying the report's margin:

<igDP:XamDataGrid.FieldSettings>

                <igDP:FieldSettings CellMaxWidth="50" />

</igDP:XamDataGrid.FieldSettings>

report1.ReportSettings.Margin = new Thickness(50, 50, 50, 50);

Let me know if you can resolve the issue with this.

Hi Vlad,

I didn't have any setting in the Report, I can assume it's already the using default value, right?

This problem only occurs when there are too many columns for one page to hold, thus after splitting to multiple pages, the last column of each page gets autofit. Is there any other possible solution to this? Thanks.