Image preview doesn't work with flysystem and dropbox.

Prereq.: Set up flysystem with dropbox as desribed in: https://doc.ezplatform.com/en/latest/guide/file_management/#native-io-handler, https://github.com/1up-lab/OneupFlysystemBundle/blob/master/Resources/doc/index.md, https://github.com/1up-lab/OneupFlysystemBundle/blob/master/Resources/doc/adapter_dropbox.md. Also generating dropbox token is required.

Steps:

1. Go to Content / Content structure.
2. Create new Image.
3. Upload valid file.
4. Publish.
5. Check preview in view mode in admin UI and on frontend.

Actual result: Preview is empty (404 in browser console). Although the file is stored on dropbox correctly.
Expected result: When using flysystem with dropbox system doesn't attempt to load images from local storage for preview.

Remarks: Affects also Image Asset field type.
Could be a missing configuration / doc issue.