Visual Composer / WPBakery中的attach_image参数允许选择多个图像

I'm building out a custom element which is just a single image. Here's how I've defined the parameters:

'params' => array(

    array(
        'type' => 'attach_image',
        'heading' => esc_html__("Image"),
        'param_name' => 'image',
        'value' => esc_html__(''),
        'admin_label' => false,
        'weight' => 0,
    )

}

According to the documentation, attach_image is used for Single image selection. However, in the admin side, I'm able to choose more than one image:

Above, I've added a yellow bg image, but get the option to add another - I only want one to be allowed (which is what I thought attach_image does).

Am I missing something here?