Basemap thumbnail none-public not working

When creating your own basemap available to your own company and uploading a thumbnail, this thumbnail cannot be used in the basemap picker. Unlike the logo functionality, the image of the basemap is not retrieved with a token and thus not accessible by the user:

Viewing the source code for the logo shows:

The thumbnail shows:

I also tested uploading the thumbnail as a logo and using that url, but that fails to.

Both items are hosted on the same portal.