Dispenser does not bonemeal Grass blocks

Yes, because the dispenser tries to use the bonemeal on a growable plant. But if there is no plant in front of it, it fails using it and so just does the "empty"-sound. Try putting a sapling or a potato (plant) in front of it and activate it then. If you want to dispense the item as item, then you have to use the dropper.

--> Works as intended

This is a new feature for dispensers where it checks for plants/crops in front of it to apply bonemeal. If you want to drop the bonemeal item itself, you can use droppers.

Stop! Why it doesn't work with grass?

Reopened until further confirmation from developers.

Put the Dispenser facing a Grass block with it's opening and it will bonemeal the grass.