In the latest builds sun is glaring everywhere, even in the basement.

Yes, I’m seeing this too. Putting sunglasses on doesn’t remove the glare debuff, either.

When I went underground, the weather report in the UI changed to say ‘underground’, but the glare debuff persisted. I haven’t seen yet if it goes away when the weather changes to cloudy or whatever.

Specifically for me:

0.A f64e68e experimental
Windows 8.1

I got the bug as well even at night and underground.
I was using the Night Vision perk as well.

Edit: using version 0.A f64e68e experimental as well