If you put an up-faced Dispenser with Bone Meal in it under a grass block, it will add "grass" on top of the grass block. if you then do it again while there already is grass on the grass block, it will use up another Bone Meal. I was working on a sheep farm design and it will not work unless this will be changed. I appreciate your attention. (I noticed it in creative but i'm sure it is the same in survival)
[Mod] Tails answered in the comments below. I am sorry to say that I am not really happy about the answer, as I may have not told the issue clearly enough. May I ask for adding a feature? because if there is no spot for any grass to spawn on anymore, I would be more then happy if it didn't use up the bonemeal, when there isn't even any changes.