Incorrect operation of the boolean operator 'cut'. Shape validation problem.

Run the script below.

pload ALL
restore Attachment 4 (BREP) part
restore Attachment 5 (BREP) tool
checkshape part
checkshape tool
bcut res part tool
checkshape res
vinit
vdisplay res -dispMode 1; vfit

Attachment 1 (PNG)
Attachment 2 (PNG)

Bug: after the 'cut' operation, we have a valid shape (checked using checkshape). But if you look through the viewer, the shape looks not valid.
Possible causes: incorrect rendering, incorrect validation, incorrect boolean operation.

Note: the input is valid.
Note: please, after finding out the reason, change the category of the task.

Also note, that the

vaspects res -setBackFaceColor RED

command does not tint the faces. If this should not be so, then please create a separate task.

Attachment 3 (PNG)