This is by design. Double-click will reset the column to its default width. You can set the default with with code like grid.DefaultRowHeight = xxx.
However the ResizingColumns event lets you implement whatever behavior you want. Here is the code snippet that autosizes the column.
private void grid_ResizingColumns(object sender, GridResizingColumnsEventArgs e)
{
if(e.Reason.Equals(GridResizeCellsReason.DoubleClick))
{
GridRangeInfo range = GridRangeInfo.Cols(1,3);
this.grid.Model.ColWidths.ResizeToFit(range);
e.Cancel = true;
}
}
Here is a little sample.