packing_box problem

[tudall]

I have a model includes a simple cubical box with several little "cubies" attached to the inside walls. puzzlecad appears to render these OK, but when the resulting STL is imported into a slicer (Bambu or Prusa) and I split the model into objects so I can reorient the pieces, two of the little interior cubies "fall off". They are separate objects, but should be attached to the packing box.
Here's the code for the box (uses default $burr_scale):
packing_box ([
"xxxxxx|xxxxxx|xxxxxx|xxxxxx|xxxxxx|xxxxxx",
"xxxxxx|xx..xx|x....x|x....x|x....x|xxxxxx",
"xxxxxx|x....x|x....x|x....x|x....x|xxxxxx",
"xxxxxx|x....x|x....x|x....x|x....x|xxxxxx",
"xxxxxx|x..x.x|xx...x|x...xx|x.x..x|xxxxxx",
"xxxxxx|x....x|x....x|x....x|x....x|xxxxxx"
], $box_wall_thickness = 6);