[Gvsig_english] DISSOLVE geoprocess error

[ernesto sferlazza]

Hello developers,
I have performed a "dissolve" geoprocessing on a shapefile of
municipalities to obtain a shapefile of provinces, based on the field
"Code_Prov" (code of the province). In the municipalities shp I have
previously calculated the area of each polygon. In the resulting
shapefile, the "sum" area of each group is very different from the sum
of the values of the polygons grouped. There is also a strange
behaviour: the value of the sum_area increases when the feature_id
increases.
If I calculate again the area of the dissolved polygon the result is
correct (and corresponds exactly with the sum of the areas of the
grouped polygons)..
I have tried both with the versions 1.1.2 and 1.9 (build 1243).
Best regards
-- 
ing. Ernesto Sferlazza
responsabile nodo provinciale di Agrigento del SITR Sicilia
resp. gruppo Sistema Informativo Territoriale
Provincia regionale di Agrigento
sede istituzionale: piazza Aldo Moro, 1 - 92100 AGRIGENTO
sede operativa: via Acrone, 27 - 92100 AGRIGENTO
cell. 3392718463 (personale)
       3316874296 (aziendale)
tel. uff 0922593752