No cap or partial cap after using slice_mesh_plane with cap=True

[baptistelabat-syroco]

slice_mesh_plane.zip
I

Trying to cap the attached mesh (in zip), I have no cap in the result (see python code to reproduce in zip). Moreover, when I encountered the problem in my code (just after saving the mesh before slicing), the behaviour was different as I got a partial cap (at the bow of the ship).

[baptistelabat-syroco]

It seems the previous mesh was not well closed. Might be the reason ? Here is another version.
KCS_mesh_closed.zip