Movement on the X an Z axis are combined?

This is probably a stupid question, but I'm trying to simply move a 3D object up, down, left, and right (Not forward or backward).

The Y axis works fine, but when I increment the object's X position, the object moves BOTH right and backwards! when I decrement X, left and forwards!

setPosition(getPosition().X + 2/*times deltatime*/, getPosition().Y, getPosition().Z); 

I was astonished that XNA doesnt have its own setPosition function, so I made a parent class for all objects with a setPosition and Draw function. Setposition simply edits a variable "mPosition" and passes it to the common draw function:

 // Copy any parent transforms. Matrix[] transforms = new Matrix[block.Bones.Count]; block.CopyAbsoluteBoneTransformsTo(transforms); 

 // Draw the model. A model can have multiple meshes, so loop. foreach (ModelMesh mesh in block.Meshes) { // This is where the mesh orientation is set, as well // as our camera and projection. foreach (BasicEffect effect in mesh.Effects) { effect.EnableDefaultLighting(); effect.World = transforms[mesh.ParentBone.Index] * Matrix.CreateRotationY(MathHelper.ToRadians(mOrientation.Y)) * Matrix.CreateTranslation(mPosition); effect.View = game1.getView(); effect.Projection = game1.getProjection(); } // Draw the mesh, using the effects set above. mesh.Draw(); } 

I tried to work it out by attempting to increment and decrement the Z axis, but nothing happens?! So using the X axis changes the objects x and z axis', but changing the Z does nothing. Great. So how do I seperate the X and Z axis movement?