The flexi-floor-Ferrari? Apparently it was
not illegal, otherwise the scrutineers would have ejected it from the Australian GP. I'm only speculating but I'd guess they are the experts on what's legal and what isn't.
Anyway, let's say the f-f-F used a liberal interpretation of the rules. The regulations were clarified after a letter from McLaren (who claim to not have had the Ferrari blueprints in March..

but instead were "told" about the floor by Nigel Stepney as a concerned "whistle-blower".
The f-f-F was modified so it fitted within the clarified rules. It's never been "illegal".
Contrast that with the Toyota rally car "turbo air restrictor" scandal (1996?) and you can see the difference.
Ralf S.