wood slabs can't be placed

Tried to place wood slabs on ground but not able to. Only in a particular 2x2 square in game.

Slabs animation appears for a fraction of a second then disappears. The slab appears to fall through the ground block on which I place it. Slab number count lowers (as if I had in fact placed slab) but doesn't show up in the 2x2 square. If I then place slabs elsewhere, slab number count increases (as if I get those slabs back).