The Nether Chest from the Nether Chested mod allows you to store items placed in it in stacks of 512 instead of the normal cap of 64. If you have a large enough sum of items in the Nether Chest, some of the items will be deleted upon sorting. For example, if you have three full stacks of Netherrack (1536 blocks) and you sort the chest, two of the three stacks will be converted into stacks of 64, reducing the sum of blocks down to 640. No matter how many stacks you're working with, one stack of 512 blocks will remain and the rest will be converted into stacks of 64 upon sorting.