TextField editor placeholder localisation

I seem to be unable to have a localised placeholder for properties edited through a text field.

  type: string
    label: i18n
    inlineEditable: true
      group: category
      position: 30
        placeholder: 'TTB.Website:NodeTypes.Category:properties.cta'

Setting the placeholder to a fixed value works just fine, however, localisation just doesn’t kick in. I’ve tried setting it to an identifier (as in the snippet above) and setting the value in the XLF file, neither of which has worked.

Am I doing something wrong or is this a bug?