my experience previously is that it is un-TOG-like (and thus an offence) to knowingly use an exploit. (And to me a bug this OP is clearly an exploit.)
What we consider in minecraft to be an exploit is more things like when there have been bugs that allowed players to duplicate items or something like that. An item freely available in the game to everyone - even if it's a mistake for it to be like that, is not an exploit in the same fashion.
But.... to add another spanner in the works....
Bazz tried to make some rubber boots today - and they don't work like they used to - so it seems they have been fixed. So basically they are now not worth making.
The ones he crafted today will wear out when you're taking damage. So while they will give you a bit extra health, they are not impervious to damage any more.
I got MiniObsi to log on and try to make some, to see if it was updating the launcher that changed them (her launcher hasn't ever been updated) - the ones she made are likewise nerfed. So it would seem that anyone trying to make boots now, will have nerfed ones. So it must be something updated on the server.
Which has the additional problem of what do we do now. Because if some people's rubber boots are the original overpowered ones, and new players can't make them like that - then yes, that is unfair advantage.
So we might have to require all players to hand in any of the old boots, so that nobody has the old impervious boots?