extrude in subtractive mode ignores both parameter

[lorenzncode]

import cadquery as cq

w, l, h = 50, 20, 15
lsnap = 8
rsnap = 0.5

s = cq.Sketch().circle(rsnap)

b = (
    cq.Workplane()
    .box(w, l, h)
    .tag("box")
    .faces("<Y")
    .vertices("<X and >Z")
    .workplane(centerOption="CenterOfMass", offset=-l/2)
    .center(0, -2.0)
    .placeSketch(s)
    .extrude(lsnap, combine="a", both=True)
    .center(0, -3.0)
    .placeSketch(s)
    # subtractive, both is ignored
    .extrude(lsnap, combine="s", both=True)
)