To reproduce:
1. Open attached project "AnimatorKeepsObjectActive.zip"
2. Open and play "testScene" scene.
3. Look at the console. Image was deactivated, but became active again. You can click left mouse button, to try to deactivate it again, but it will stay active.
4. Stop scene.
5. In Hierarchy find "canvas" -> "Container". Select "Container", open "Animator window" and delete "DisableImage" animation.
6. Open "Game window" and play the scene. Now image gets disabled by the script, as it should be.

Actual result: GameObject can't be disabled by a script, if there's Animator with animation which has GameObject.IsActive property of said GameObject. Even if animation is not connected by any transition.
Expected result: If animation is not connected by any transition, it should not effect objects.

Reproducible with: 5.3.6p7, 5.4.3p1, 5.5.0f3, 5.6.0b3