Modelling bug?

```
import cadquery as cq
from cadquery.selectors import *

from dataclasses import dataclass

# Parameters

@dataclass
class StatorParameters:
diameter: float = 51.0
hole: float = 12.0
slot_diameter: float = 2.0
slot_height: float = 5.0
slot_thick: float = 5.0
port_thick: float = 2.0
cup_thick: float = 2.0
wall_distance: float = 1.0
slot_num: int = 16

@dataclass
class MoldParameters:
gap: float = 10.0
wall_thick = 3.0

mold = MoldParameters()
stator= StatorParameters()

height = stator.slot_thick + stator.port_thick + stator.cup_thick

part = cq.Workplane('XY').polarArray((stator.diameter/2 - stator.slot_height/2 - stator.wall_distance), 0, 360, 16).slot2D(stator.slot_height, stator.slot_diameter).extrude(stator.slot_thick)

part = part.faces('>Z').workplane().polarArray((stator.diameter/2- stator.slot_diameter/2 - stator.wall_distance), 0, 360, 16).circle(stator.slot_diameter/2).extrude(stator.port_thick)
```