How to change RenderSettings.skybox correctly in Unity5?

Hello All. There is a problem setting the skybox material at run time. I use this code to change it:

RenderSettings.skybox = _skybox; //Material

then as manual says I call

Code (CSharp):

1.  /* If you change the skybox in playmode, you have to use the DynamicGI.UpdateEnvironment function call to update the ambient probe. */
2. DynamicGI.UpdateEnvironment ();

But it does not update reflections. :-/
It only resets reflections when I pass null as the new skybox material, And when later I set existing material back nothing happens (the skybox image changes, but the reflections don't exist anymore).

I noticed that if I do it in editor, and then touch defaultReflectionMode (switch it to Custom, then back to Skybox), everything updates according to the new skybox. And in the status bar I see the message "1/3 Reflection probes | 1 jobs". But I do not use any reflection probes!
I tried this in the script, but with no luck:

Code (CSharp):

1.     //touch the reflection type to accept the new skybox
2.     RenderSettings.defaultReflectionMode = DefaultReflectionMode.Custom;
3.     RenderSettings.defaultReflectionMode = DefaultReflectionMode.Skybox;

It looks like it has some hidden reflection probe somewhere, and inits it when I set defaultReflectionMode = Skybox (manually).
So, the question is - what function does it call to create this hidden probe, and is it accessible in the play mode?
I've tried this in versions 5.2.4, 5.6.7 - same results.

Now I'm totally lost. Is there a correct way to change the skybox material at runtime with correct reflections?