[![enter image description here][1]][1]

The image above shows a mesh with a sphere shape.  It is symmetric about the 3 axis similar to a cube.  Note the red faces have a 3 corner not a 4 corner. Not a UV Sphere.  The mesh will work symmetrically along x, y, z axis with a cast cuboid modifier.

In the image in your original question concentric rings of the UV Sphere are placed along the z-axis.  Speaking about the default situation.  So the there is an asymmetry regarding the z-axis.  So the mathematics amplifies this asymmetry.  You will get slightly better results if you subdivide your mesh again.

You can edit the sphere in [edit] mode and rotate 90 on the y axis.  The asymmetry deformation will be rotated as well.

I will place a better [cast] image here in a moment.


  [1]: https://i.sstatic.net/ZXcf6.png