Image filter with media.yaml does not work

[Rotzbua]

Environment

Grav: 1.5 and 1.6
php 7.1

Bug

Added grayscale filter to media.yaml.

Expected:
Grayscale pictures

Observed:
No change

Any image filter defined in media.yaml are not used.
Seems it is the old #984 .

Reproduce & test

Used: default media.yaml
Paths: system/config and user/config

Modified:

types:
  defaults:
    type: file
    thumb: media/thumb.png
    mime: application/octet-stream
    image:
      filters:
        default:
          - grayscale

Also changed:

  jpg:
    type: image
    thumb: media/thumb-jpg.png
    mime: image/jpeg
    filters:
      - grayscale
  jpe:
    type: image
    thumb: media/thumb-jpg.png
    mime: image/jpeg
    filters:
      - grayscale
  jpeg:
    type: image
    thumb: media/thumb-jpg.png
    mime: image/jpeg
    filters:
      - grayscale

Images do not change at all.