Multiple split with Faces produce inconsistent results

We are trying to generate multiple cuts to 'raster' basic geometries
The sample code below produces inconsistent results with missing parts of the split ellipsoid

```python
import cadquery as cq
import numpy as np

a_x=0.15
a_y=0.31
a_z=0.4
grid=[4, 4, 4]

transform_mat = cq.Matrix(
[
[a_x, 0, 0, 0.],
[0, a_y, 0, 0.],
[0, 0, a_z, 0.],
]
)

sphere = cq.Solid.makeSphere(1.0, cq.Vector(0, 0, 0), angleDegrees1=-90)
ellipsoid = sphere.transformGeometry(transform_mat)

solidList = []

for solid in ellipsoid.Solids():
wk_plane = cq.Workplane().add(solid)
xgrid = np.linspace(-0.5, 0.5, num=grid[0], endpoint=False)[1:]
ygrid = np.linspace(-0.5, 0.5, num=grid[0], endpoint=False)[1:]
zgrid = np.linspace(-0.5, 0.5, num=grid[0], endpoint=False)[1:]
print(ygrid)
for i in xgrid:
Plane_x = cq.Face.makePlane(None, None, basePnt=(i, 0, 0), dir=(1, 0, 0))
wk_plane = wk_plane.split(cq.Workplane().add(Plane_x))
print('x:', len(wk_plane.val().Solids()))
for j in ygrid:
Plane_y = cq.Face.makePlane(None, None, basePnt=(0, j, 0), dir=(0, 1, 0))
wk_plane = wk_plane.solids().split(cq.Workplane().add(Plane_y), keepBottom=True, keepTop=True)
print('y:', len(wk_plane.val().Solids()))
for k in zgrid:
Plane_z = cq.Face.makePlane(None, None, basePnt=(0, 0, k), dir=(0, 0, 1))
wk_plane = wk_plane.split(cq.Workplane().add(Plane_z), keepBottom=True, keepTop=True)
print('z:', len(wk_plane.val().Solids()))

for subsolid in wk_plane.val().Solids():
solidList.append(subsolid)

compound = cq.Compound.makeCompound(solidList)
cq.exporters.export(compound, "compound.step")
```


It is however expected to keep all the split solids
a grid of [5,5,5] provide expected results :