Steps to reproduce
Open a creative world (this can also be reproduced in multiplayer or with commands)
Type /achievement give achievement.acquireIron (as thats the achievement before DIAMONDS)
Get a diamond block and craft it to get 9 diamonds, put those diamonds in your inventory
Repeat this on a separate world but this time try smelting diamond ore to acquire the diamond
(Basically the bug here is that you can only get the achievement can only be obtained when the diamond is picked up from the floor rather than transferred directly into the inventory, something that doesn't seem to apply to any other resources (e.g. logs, iron...) )
Comments 9
The achievement is "Acquire diamonds with your iron tools" and not "Smelt diamond ore in an oven" or "Break a block of diamond"
Aha! Read the MCwiki page on achievements, for the DIAMONDS achievements it says 'pick up diamonds from a crafting table or the ground' http://minecraft.gamepedia.com/Achievements
also, if it is only pick up a diamond to get the achievement, that is also a bug, on multiplayer you may well be given a diamond block, or on singleplayer you may get a silk touch pickaxe and mine diamond ore with it, but dont get an achievement for either
...and the tooltip in-game says "Acquire Diamonds with your iron tools".
I fixed the wiki page for you.
The tooltip says many things. The Acquire Hardware achievement can be earned simply by picking up an iron ingot, but the tooltip says smelt iron ore to get an iron ingot.
The Achievement "Acquire Hardware" cannot be obtained via just picking up an Iron Ingot. This is even on the wiki.
The point is, you can acquire diamonds by using a silk touch pick on diamond ore and then smelting it or by being given a diamond block on multiplayer, and neither will get you the achievement even though you rightly got diamonds
Probably intended, as you normally get your first Diamonds via mining them or picking them up from the floor from a friend.