Preconditions:

Created content type with required field textline and non required file (max file size is empty).

Steps:

1. Create content item with content type from preconditions.
2. Fill the textline and upload a file bigger than 5 MB.
3. Click Publish.
4. Go to Content structure/Content types/Content and edit content type from preconditions.
5. Set max file size for file for ex: 2 MB. Save.
6. Go to edit mode of content item created in step 2.
7. Edit textline.
8. Click Publish.

Actual result:

File field is cleared, validation message is displayed. It works the same for image and media field.

Expected result:

File should not be removed, except when user upload a new one. 

UX comment: Validation should appear with info that file is too big. Image shouldn't be removed.