Everything falls back to ground material, except glass...

When breaking a block with the right tool, we are able to pick it up. Sand however can be melted into glassblocks or glasspanes. Sand is therefor breakable and re-usable but when we make glass and break it, nothing leaves behind. I find this a mathematical bug because if you break glass you get splinters and should be able to make the same glassblock or glasspane in a furnace whole again. It seems fair!