O'Reilly's Learning XNA 4.0 - Camera not functioning properly.

Good evening fellows, I recently started reading the book O'Reilly Learning XNA 4.0 and i'm at the 3D camera movement. I noticed something wrong was happening with the camera, when i pitch up and down fast it begins to pitch slower to the point it stops and everything disappears. I don't know why this is happening because i'm new to the subject and i'm trying to find some answers. If anyone needs the code to know what i'm talking about here it is.

// Pitch rotation
cameraDirection = Vector3.Transform(cameraDirection, Matrix.CreateFromAxisAngle(Vector3.Cross(cameraUp, cameraDirection), (MathHelper.PiOver4 / 200) * (Mouse.GetState( ).Y - prevMouseState.Y)));
cameraUp = Vector3.Transform(cameraUp, Matrix.CreateFromAxisAngle(Vector3.Cross(cameraUp, cameraDirection), (MathHelper.PiOver4 / 200) * (Mouse.GetState( ).Y - prevMouseState.Y)));