Dan

Well, if it's just chipboard, I'd think it's risky too, but the boards you talk about are T&G chipboard floors designed with a load bearing weight allowance thingy me bob. So they can carry weight like tiles and people etc. They're also improved from a 'getting wet' point of view too, whcih means the adhesives shouldn't weaken them, which is what would happen with usual chipboard eventually if you tiles to it directly and water kept soaking through the grout joints and then in to the adhesive and then in to the chipboard.

Dan