I was eating a carrot in minecraft on the environment listed above, and I ate one, but could not eat any more. I think this is due to the player using the use item button and the game getting it mixed up with other entities. I.e, I want to eat the carrot, but the game thinks I want to right click on the grass block. 

To trigger:

Hold more than one carrot in hand.

Have at least 4 hunger points missing.

hold down use item while looking at a block of any kind.