Stone slabs cannot be included in custom villager trades

Verification Build 1.12.0 Windows 10. (won't let me choose anything except future versions from affected versions dropdown).

I've been putting together several trading shops and have discovered that trade tables work absolutely fine unless stone_slab, stone_slab2, stone_slab3 or stone_slab4 items of any damage value are included as an item offered by the villager. wooden_slab seems to work fine.

To reproduce:
1. Create a new creative world and apply a new resource pack with the attached stonemaker_trades.json file under `trading/economy_trades`.

2. Edit the `villager_v2.json` behavior file in the behavior pack so that at least one variant of villager uses the stonemaker trade table.

3. Summon a villager into the world that uses this trade table. The trade window will correctly show all of the trades listed in the table.

4. Exit the world, then within the `trades` array of the `stonemaker_trades.json` file, add this additional trade object:

{
  "num_to_select": 1,
  "trades": [
    {
      "wants": [
        {
          "item": "minecraft:gold_nugget:0",
          "quantity": 1,
          "price_multiplier": 0.05
        }
      ],
      "gives": [
        {
          "item": "minecraft:stone_slab3:1",
          "quantity": 15
        }
      ],
      "trader_exp": 0,
      "max_uses": -1,
      "reward_exp": false
    }
  ]
}

5. Re-open the world and summon a NEW villager that uses this trade table.

Observed Results: The trades of the new villager will now be blank, missing both the slab and any other trades.

Expected Results: The trade window should have a selection of blocks to trade, including the slab trade.