Attribute "simplifyFieldListFolders" is not working

Hello,
While using a Power BI Premium dataset as data source (which should count as SSAS or Azure Analysis Services data source), I find this field not to be working properly.
I want all the folders to show up on the Field List, including the folder containing only one attribute (instead of having them in the root folder). It is important because of the naming convention we use.
When I add it to my Flexmonster instance, it does not make any difference. This is the code I am using:

let reportString = {
  "dataSource": {
    "type": "microsoft analysis services",
    "proxyUrl": "xxxxx",
    "catalog": "xxxxx",
    "cube": "Model",
    "binary": true,
  },
  "slice": {
    "expands": {
      "expandAll": true
    },
    "drills": {
      "drillAll": true
    }
  },
  options: {
    "simplifyFieldListFolders": false,
    "configuratorActive": true,
    "useOlapFormatting": true
  } 
}

I attached a screenshot showing the issue. You can see there 3 folders and 5 attributes not belonging to any folder. Each of these 5 attributes should be in a folder.