I have a problem with qgis 2.8.1 (Wien). Whenever I change the project SRC to WGS84-World Mercator (EPSG 3395), the area is calculated as zero.
How can I solve this problem? Is this a known bug?
The answer from How can I get my Qgis area calculations in metres rather than degrees? My shapefiles are projected using WGS 1984 UTM fuseau 35 Sud don't solve the problem, since the problem only appears with a metric CRS.