Steps to reproduce:

1. Edit ezpublish/config/config.yml, reset default image aliases and add a few test ones:

parameters:
    ezsettings.ezdemo_site_admin.image_variations: {}
    ezsettings.ezdemo_site_admin.image_variations:
        reference:
            reference: null
            filters:
                - { name: geometry/scaledownonly, params: [800, 800] }
        small_custom:
            reference: reference
            filters:
                - { name: geometry/scaledownonly, params: [150, 300] }

Note: in this case, the admin siteaccess name is "ezdemo_site_admin". Please adapt as necessary.

2. On the admin interface, go to /setup/ini settings, select image.ini and the admin siteaccess from list. You should see the following:

[AliasSettings]
AliasList		injected		[0] reference
			injected		[1] small_custom
...

3. Create/edit an article, go to "body" field and click on the "Insert / edit image" icon.
4. Search or browse for existing images. The returned images will be disabled, making image selection impossible.

Note: uploading new images will work, though.