"Write defaults" off/on seem to always write defaults

I have a script which controls the eye position (mouse tracking)
I have a non-active animation which would under specific circumstances control the eyes in a loop

now when the eye-animation is not running I would like to control the eyes via mouse.

So I though I could prevent the Animator to reset the eye values all the time by having all states "write defaults" turned off, but the Animator still does it.

I made a video thats shows the problem
http://mindart.de/writedefaults.mp4

I think I misunderstand the "write defaults" option a bit.
Could anybody give me a hint?

Unity 5.3.2p3