UnProject fails to get the world coordinate when scaling - opengl

Question

In my SharpGL project (C#) I have used the Unproject function in order to get the world coordinates from mouse coordinates.
This procedure, quite trivial, fails when the drawing is scaled. I found many articles about this issue, but no one suited me.
When I say scaled means that in draw main proc i apply this code:
_gl.Scale(_params.ScaleFactor, _params.ScaleFactor, _params.ScaleFactor);
Then, when I intercept the mouse move I want to visualize the world coords. These coordinates are precise when the scale factor is 1, but when I change it these are wrong.
for example:
a world point (10, 10)
scaled 1 is detected (10, 10)
scaled 1,25 is detected (8, 8)
scaled 1,25 is detected (6.65, 6.65)
This is my simple code, consider that scale_factor is just passed for debugging.
public static XglVertex GetWorldCoords(this OpenGL gl, int x, int y, float scale_factor)
{
double worldX = 0;
double worldY = 0;
double worldZ = 0;
int[] viewport = new int[4];
double[] modelview = new double[16];
double[] projection = new double[16];
gl.GetDouble(OpenGL.GL_MODELVIEW_MATRIX, modelview); //get the modelview info
gl.GetDouble(OpenGL.GL_PROJECTION_MATRIX, projection); //get the projection matrix info
gl.GetInteger(OpenGL.GL_VIEWPORT, viewport); //get the viewport info
float winX = (float)x;
float winY = (float)viewport[3] - (float)y;
float winZ = 0;
//get the world coordinates from the screen coordinates
gl.UnProject(winX, winY, winZ, modelview, projection, viewport, ref worldX, ref worldY, ref worldZ);
XglVertex vres = new XglVertex((float)worldX, (float)worldY, (float)worldZ);
Debug.Print(string.Format("World Coordinate: x = {0}, y = {1}, z = {2}, sf = {3}", vres.X, vres.Y, vres.Z, scale_factor));
return vres;
}

Answer 1

I found a solution!
there were in the main draw procedure a portion of code that alterate results of UnProject function.
gl.PushMatrix();
.Translate(_mouse.CursorPosition.X * _params.ScaleFactor, _mouse.CursorPosition.Y * _params.ScaleFactor, _mouse.CursorPosition.Z * _params.ScaleFactor);
foreach (var el in _cursor.Elements) //objects to be drawn
{
gl.LineWidth(1f);
gl.Begin(el.Mode);
foreach (var v in el.Vertex)
{
gl.Color(v.Color.R, v.Color.G, v.Color.B, v.Color.A);
gl.Vertex(v.X, v.Y, v.Z);
}
gl.End();
}
gl.PopMatrix();