Apologies if this is working as intended but the mass of a tile is suspiciously halved after digging it up.
I have tested it with Sandstone, Dirt, Sand, Copper and Coal and the mass of the pile left on the ground is always half of the original mass.
See attachments for details.
Hover over and check the details of a tile before digging it up. Hover over and check the details of the resource pile of the same tile after digging it up.