Syntax for list items in en.yaml translations for Add-On configurations

I wrote an Add-on, HAOS-Kiosk, (HAOS-kiosk/haoskiosk at testing · puterboy/HAOS-kiosk · GitHub) and am having trouble getting it to respect the translations for list items in the Configuration.

Specifically, I am using translations/en.yaml to among other things capitalize the names of the list buttons in the Add-On Configuration UI. All the other translations lines (Name, Description) work fine. Just the items: list has no effect.

The relevant lines of my config.yaml are:

options:
  ha_url: "http://localhost:8123"
  ha_dashboard: ""
  login_delay: 1.0
  zoom_level: 100
  browser_refresh: 600
  screen_timeout: 0
  hdmi_port: 0
  ha_theme: "dark"
  ha_sidebar: "none"

schema:
  ha_username: str
  ha_password: password
  ha_url: str
  ha_dashboard: str?
  login_delay: float(0,)
  zoom_level: int(10,1000)
  browser_refresh: int(0,)
  screen_timeout: int(0,)
  hdmi_port: int(0,1)
  ha_theme: list(auto|dark|light|none)
  ha_sidebar: list(full|narrow|none)

And the relevant lines of translations/en.yaml are:

configuration:
  ha_theme:
    name: "HA Theme"
    description: "Display theme [Default: Dark]"
    items:
      auto: "Auto"
      dark: "Dark"
      light: "Light"
      none: "None"
  ha_sidebar:
    name: "HA Sidebar"
    description: "Status of left sidebar [Default: None]"
    items:
      full: "Full"
      narrow: "Narrow"
      none: "None"

yamlint shows no syntax or whitespace errors in either config.yaml or en.yaml – and everything else in both files works as expected.

However, the labeling of the list item buttons remain uncapitalized

Any thoughts on what I might be doing wrong?
Note: I did not find much documentation on how to do translations for list items so I may be doing it wrong