Wrong response body (Cart API) when adding cart item to cart

[Jujuba]

When creating a cart (via API) with a product, which has an automatic discount applied like "Buy 3(n) and get 10% off", the (n+1) product added is not added to the cost of the line item.

Creating cart with product X

mutation {
  cartCreate(
    input: {lines: {merchandiseId: "gid://shopify/ProductVariant/44134907969855", quantity: 1}, buyerIdentity: {countryCode: DE, deliveryAddressPreferences: {deliveryAddress: {firstName: "Max", lastName: "Mustermann", country: "Germany", city: "Musterstadt", zip: "83772", address1: "Musterstrasse 1"}}}}
  ) {
    userErrors {
      message
    }
    cart {
      checkoutUrl
      id
      cost {
        totalTaxAmount {
          amount
        }
        totalAmount {
          amount
        }
        subtotalAmount {
          amount
        }
      }
      lines(first: 1) {
        edges {
          node {
            quantity
            id
            sellingPlanAllocation {
              priceAdjustments {
                price {
                  amount
                }
              }
            }
            merchandise {
              ... on ProductVariant {
                image {
                  url
                }
                title
                id
                price {
                  amount
                }
                sellingPlanAllocations(first: 1) {
                  edges {
                    node {
                      priceAdjustments {
                        price {
                          amount
                        }
                      }
                    }
                  }
                }
              }
            }
          }
        }
      }
    }
  }
}

Adding a single product X to the cart

mutation {
  cartLinesAdd(
    cartId: "gid://shopify/Cart/c1-df9ac8e71b99a136405e930b4d60e44f"
    lines: {merchandiseId: "gid://shopify/ProductVariant/44134907969855", quantity: 1}
  ) {
    userErrors {
      message
    }
    cart {
      checkoutUrl
      id
      cost {
        subtotalAmount {
          amount
        }
        totalAmount {
          amount
        }
      }
      lines(first: 30) {
        edges {
          node {
            quantity
            id
            merchandise {
              ... on ProductVariant {
                image {
                  url
                }
                title
                id
                price {
                  amount
                }
              }
            }
            sellingPlanAllocation {
              sellingPlan {
                id
              }
              priceAdjustments {
                price {
                  amount
                }
              }
            }
            cost {
              totalAmount {
                amount
              }
              amountPerQuantity {
                amount
              }
              compareAtAmountPerQuantity {
                amount
              }
              subtotalAmount {
                amount
              }
            }
            discountAllocations {
              discountedAmount {
                amount
              }
            }
          }
        }
      }
    }
  }
}

Example response adding 6 items of a product X with has a automatic discount applied "Buy 5 and get 20% off".

As you can see, the cost of the 6th item is not added to the cost of the line item. The quantity is added.