I need more crafting tweaks help...

I am simply confused:
This recipe works:
{
    "type": "minecraft:crafting_shaped",
    "pattern": [
        "#  ",
        "## ",
        "###"
    ],
    "key": {
        "#": {
            "item": "minecraft:acacia_planks"
        }
    },
    "result": {
        "id": "minecraft:acacia_stairs",
        "count": 8
    }
}
and this one doesn't:
{
    "type": "minecraft:crafting_shaped",
    "pattern": [
        "#  ",
        "## ",
        "###"
    ],
    "key": {
        "#": {
            "item": "minecraft:oak_planks"
        }
    },
    "result": {
        "id": "minecraft:oak_stairs",
        "count": 8
    }
}