First was mining very far from spawn point, had maybe one slot open in inventory when I found the diamonds (mining with diamond pick axe). Saw the diamond sprite drop, heard the sound effect of picking it up. Mined maybe 3 blocks and left. Later I checked inventory and there were no diamonds. Second time (saved and opened on a diff day) found some diamonds, checked to make sure I had open slots in the inventory, again with a diamond pick axe, saw the diamonds drop, drawn toward me and disappear, after mining a few blocks check inventory, no diamonds to be seen. On a third day after game closings and openings, found diamonds again, mined one block with diamond pick axe, 5-7 open inventory spots, checked after drawing in the diamond sprite, no diamond in inventory. I went to a chest and emptied all my inventory except the diamond pick axe, and 2 other items all in quick access. Mined another block (1) in the same vein of diamonds and instantly found 12 diamonds in inventory. Seemed to be all the diamonds found on previous efforts. Additional mining of diamonds all added properly then.