New Post: About reprojection

Dear All,
I'm working with a collegue of mine, he is the developer and I'm the GIS man.

We have some problems with projection and reprojection, and then he told me: "write you this email" ;)

We define the map projection of the project reading this .prj file:
PROJCS["Popular_Visualisation_CRS_Mercator_deprecated",GEOGCS["GCS_Popular Visualisation CRS",DATUM["D_Popular_Visualisation_Datum",SPHEROID["Popular_Visualisation_Sphere",6378137,0]],PRIMEM["Greenwich",0],UNIT["Degree",0.017453292519943295]],PROJECTION["Mercator"],PARAMETER["central_meridian",0],PARAMETER["false_easting",0],PARAMETER["false_northing",0],UNIT["Meter",1],PARAMETER["standard_parallel_1",0.0]]

It's EPSG:3785 (http://prj2epsg.org/epsg/3785).

Then I add a shapefile coupled with this .prj file:
PROJCS["WGS84_/_UTM_zone_33N_(CM_15E)",GEOGCS["WGS84_/_Geographic",DATUM["D_WGS_1984",SPHEROID["WGS_1984",6378137.0,298.2572235630,AUTHORITY["EPSG","7030"]],AUTHORITY["EPSG","6326"]],PRIMEM["Greenwich",0.0],UNIT["Decimal_Degree",0.01745329251994330]],PROJECTION["Transverse_Mercator"],PARAMETER["Latitude_Of_Center",0.0],PARAMETER["Longitude_Of_Origin",15.0],PARAMETER["Scale_Factor",0.9996000000],PARAMETER["False_Easting",500000.0],PARAMETER["False_Northing",0.0],UNIT["Meter",1.0],AUTHORITY["EPSG","32633"]]

It's EPSG:32633 (http://prj2epsg.org/epsg/32633), dotSpatial read it properly and then we force the reprojection to EPSG:3785. The problem is that the projected coordinates are wrong.

If instead we set the coordinates system of the shp file we want to add using the code below, and then reproject it to EPSG:3785 we have the right projected coordinates

Why we have different these different behaviours?

Thank you very much,

Andrea