My sims twinkle at night even without any windows if there is a burning fireplace in the room and I move my mouse. Not sure if its the same bug but what it seems to be is the graphics reset as the mouse is moving, as if the various fire lighting phases are being cycled through as the mouse moves. As I said before, may not be the same issue as yours is with a window instead of a fireplace but could be why the flickering is happening, with various light phases being cycled through. In my case, the flickering stops when I stop moving the mouse or remove the fireplace. This is not a big issue for me but have included it in case it provides a clue for the before mentioned issue.
Edit, I forgot to mention, I noticed this while the game was paused as well as if running.
There's a lot of twinkle going on now. You might wanna post here instead http://answers.ea.com/t5/The-Sims-4-Bug-Reports/Sim-flashing-after-new-update/td-p/4999959/jump-to/first-unread-message
