I was playing in creative mode and I was trying to make a sorting machine with redstone and hoppers, then I attached item frames on stairs to indicate each items in chests. After a while, those item frames seemed to be disappeared, press R (pick block) on the original item frame area got me the stair behind, putting another item frame is not possible, but still costed me one item frame if I am putting another item frame in survival mode. When the stair block was deleted, the item frame and the item originally in the item frame reappears as entities.
PS: Stairs are used so that I can access the chests located below the stair, other blocks are not tested yet. Sorry if this issue was reported before.