This was an oddity I encountered today while building a very tall tower in Vaisier. I forgot to kick in infinite blocks mode, and ran out of stone. No worries, I thought–I’ll just harvest one back and continue in infinite mode.
I could destroy the stone and collect the orange cube, but it wouldn’t show up in my inventory at all. I deleted some repeat blocks, had room in the inventory and on the item bar–but even though the game made the collection noise the stone never showed up. I finished the tower with bricks. The screenshot has the coordinates in it, if that helps any.