Aye, they apparently removed the backwards transmutation from the minium stone.
You can upgrade 8 iron to gold, you can't downgrade 1 gold to iron. Seems to be across the board and there are other restrictions. Couple exploits this fixes:
1. No more infinite iron from downgrading ender pearls or gold from a T5 spawner.
2. No more infinite blaze rods from transmuting 2 dust to a rod (disabled now) and then pulverizing it back to dust.
3. No more infinite bone meal from transmuting 3 meal to a bone (disabled now) and then pulverizing it back to dust.
Edit: Hmm, though relogging does re-enable the backwards transmutation.
So there's a bug somewhere; either backwards transmutation just bugs out and the recipes disable themselves or they intend to disable those recipes and relogging bugs it out by re-enabling them.
Given that the recipes affected are the exploitable ones, I'd guess it's the latter.