When you have planted crops and go adventuring the crops will stop growing if you move too far away and will still be at the same growth stage when you get back. I'm guessing this is because blocks are unloaded when you move further away. As far as I am aware this effects every kind of crop, including cocoa and melons, etc. I don't know if you want to fix this but one way might be to make a note of the game time when you plant a crop and then compare that to the actual time when the block is reloaded.