Sigh. Any construction relies on its user’s mental capacity and on the constructor’s foresight.
I’ve now replaced the basket with a cardboard box. I fastened the box with nails to the white shelf, and it has stayed on its place (at least until now). Cardboard isn’t of course the best material for nailing, so I’ll invest in a wooden box if this doesn’t work out.
Are you ever done with cat-proofing?!? (Not 100% sure if I really want to hear your answers and stories to this question… hehehe)