The problem with the skeleton challenge is because your inventory is full when you do it. The code must be written to give you the reward a split second before removing the items. Because the challenge requires 36 stacks your inventory will be full of items. It doesnt just drop the egg on the floor it just errors out and doesnt give it.
Or, you know, you could bonemeal a bunch for oxeye daisies and azure bluets... those also give light grey dye.
