App "icon.png" in locale folder ignored by client

• Device OS and version: Android 6.0.1
• Device model/manufacturer: OnePlus 2, OxygenOS 3.6.1
• F-Droid version (in the About screen): 1.2.2
• F-Droid privileged extension version (if installed):

I have successfully created my own fdroid repo at https://fdroid.xbrowsersync.org/fdroid/repo/ to just host the apk for my app (cannot build it via fdroid as it's a cordova app). However, when I add the repo to my fdroid client and search for my app, the screenshots and feature images are displayed but the app icon is not, as this screenshot shows:

I used the fastlane supply folder structure in my repo to add the images like so:

repo
 |_ com.xBrowserSync.android
     |_ en-US
         |_ featureGraphic.png
         |_ icon.png
         |_ phoneScreenshots
             |_ Phone_1.png
             |_ Phone_2.png
             |_ Phone_3.png
             |_ Phone_4.png
             |_ Phone_5.png   

The images are accessible from the web:

• featureGraphic.png: https://fdroid.xbrowsersync.org/fdroid/repo/com.xBrowserSync.android/en-US/featureGraphic.png
• icon.png: https://fdroid.xbrowsersync.org/fdroid/repo/com.xBrowserSync.android/en-US/icon.png
• etc

The localized property in the repo index-v1.json file does show the icon property correctly:

"localized": {"en-US": {"featureGraphic": "featureGraphic.png", "icon": "icon.png", "phoneScreenshots": ["Phone_1.png", "Phone_2.png", "Phone_3.png", "Phone_4.png", "Phone_5.png"]}}

Am I missing something or is this a bug with the client?