TableRow which has defined an only val attribute of the trHeight is imported as a row with auto height. By the specification, this is right, but MS Word takes the val value as row height. Also MS Word exports "At Least" row height with only 'val' set.

Workaround: Iterate through the table rows and set them HeightType to Exact or AtLeast:

foreach (var row in this.document.EnumerateChildrenOfType<TableRow>())
{
    row.Height = new TableRowHeight(HeightType.AtLeast, row.Height.Value);
}