When I save a .shp file as .kml and keep the DescriptionField as "Description", the Description field in the attribute table is blank, but when the DescriptionField is set to "Descriptio" (no "n" character on the end), the Description field is properly completed.
Have you tried using the export to kml tool in mmqgis plugin? This allows you to specify columns for export.
From the authors web site: This tool exports features to KML with the capability to explicitly specify fields for the Name and Description that are always displayed in the current (as of this writing) default Google Maps (tm) interface.
Multiple fields can be combined in the description. The Description Separator indicates how multiple fields should be separated: as separate paragraphs, preceded by a field name in separate paragraphs, or simply separated by commas in a single paragraph.