Table description NOT GENERATED for Label.class column property


I have a
problem with adding a Description to my FilterTable
object (add-On, Table extension). I use ItemDescriptionGenerator interface (ovverride generateDescription method). It does work OK for columns of String/Double/Timestamp.class property, but
failed to add a Description to column which property is of Label
(a lightly-changed Label.class extension). I use Vaadin 6.

It seems that ItemDescriptionGenerator even does not “touch” this property (I printed “touched” columns’ property names). WHY? Any solution???
Thank you for help in advance!