QGIS » QGIS Application

When adding a shapefile which does not have a .prj attached, QGIS determines the CRS for that layer either by the Global CRS (in Settings->Options->CRS) or by the user choosing the CRS.
In order to then add the correct *.prj file to that shapefile, the fTools "Define Current Projection" should be used. However, the tool fails with the error: "Identical output coordinate reference system".
In other words, you *cannot create a *.prj for a shapefile when the CRS chosen on loading the shapefile is the same CRS that should be saved to the *.prj.

Correct behavior should be:

Once the shapefile is loaded (and it's CRS is known to QGIS by either of the above options) the "Define current projection" should just output a correct *.prj based on the CRS chosen by the user, with nothing more than an information window saying:

"Creating a *.prj file for xxxx.shp based on CRS...."

with an OK-Cancel button.