When your graphic settings in 'Video Settings' of the Options is on 'Fast', I have noticed that leaves differ from being in inventory and when placed into the world, the leaves that are in the world, are not transparent (Fast), but those in the inventory are transparent (Fancy). Here is an attachment to prove what I mean. During 1.7, I think that leaves in your inventory change according to your graphic settings, if not, 1.5 or even 1.6.