Bug, mod, or normal? After game starts, lighting changes when I first move

[Holdstrong]

I'm chasing down something that is driving me nuts, and I'm starting to think this is just the way the game is... and I never noticed it before. But I'd like to try to confirm that.

When I start a game, everything looks a certain way in terms of lighting... and then when I move my character for the first time. BOOM. Lighting changes. Sometimes it is subtle, just a change in shadows, sometimes it is jarring and can go from a very light day to pretty dark.

Here is a subtle example: https://imgur.com/a/lighting-changes-nnkJK7B

I was convinced this must be a lighting or weather mod doing it - and maybe those things do make it more obvious to notice. But I can actually see it happening on a new, unmodded game launched from the Steam launcher.

Here is how I reproduce it:

1. Launch the game
2. Open console from the main menu and type 'coc guardianstones'
3. You start off facing the stones and they look a certain way, with certain lighting, depending on the random weather that loaded. Take note of how they look and keep looking at them and then...
4. Take one step forward and notice how that lighting changes.

It is more obvious on sunny days. Some very overcast days don't seem to do it (or it is too subtle for me to see).

Is this normal or something that is known? If not, any ideas how to track it down and try to resolve it?