When crafting chests it will display an unusually shadow change on the blocks in inventory. It only happens when crafting chests i found.
As you can see the shadow appears on the right at first, then once the chest recipe is put in the shadow changes to the left side of all the blocks in the inventory.
NOTE: I also found out later that just picking up a chest and moving it around in the inventory, chests, crafting tables, etc causes the light glitch as well.
It is in fact a Lightning Bug. If you look in the inventory in 16w21a snapshot, you can see the shadows are on the right instead of the left. But when crafting, the item (chest) appears to have a shadow on the left. This happens because maybe the item wasn't changed when you crafted the item(chest). This might be fixed in the next update.