Attribute Term & menu_order

I’m having an issue with menu_order on my (via API) created Attribute terms.

I’m sending this:

{
  "create":[
    {
      "name":"XXS",
      "menu_order":1
    },
    {
      "name":"XS",
      "menu_order":2
    },
    {
      "name":"S",
      "menu_order":3
    },
    {
      "name":"M",
      "menu_order":4
    },
    {
      "name":"L",
      "menu_order":5
    },
    {
      "name":"XL",
      "menu_order":6
    }
  ]
}

and in the response, I get echoed back the proper menu_orders. However, in my WooCommerce site, they appear in alphabetical order:

L
M
S
XL
XS
XXS

The “Attributes” menu item lists the “Size” attribute as “Custom Ordering” (and the terms in the above order).

If I go in and manually drag/drop the items to my preferred order (XXS/XS/S/M/L/XL) it works, but I’d like to be able to set it via the API.