Whenever you try to apply changes in the Sprite Editor window, the "Unapplied Import Settings" warning popup will always come up. This will also happen if you close the Sprite Editor without making any changes at all.

This is a regression from 2018.2

Tested on 2018.2.0b9, 2018.3.0a1, 2018.3.0a2

1. Install Unity
2. Open the attached project
3. Select "TestSprite" from the Project view and open the Sprite Editor
4. Make some changes that will require Applying e.g. make some slices
5. Apply the changes

Result:
A warning popup appears telling you that there are unapplied import settings and that the asset has been modified outside the Sprite Editor.

Expected Result:
Changes are applied without warning.