Low fps in a certain place in my hideout

I just created a new hide out with Zana. I noticed that the fps drops from 120 to 33 on a lower left side of the main area. I noticed that when I deleted all the lamps and fires from the hideout the fps drop went away. I also noticed that when the lamp/fire was just on the edge of my screen, the fps dropped or fluxuated. I guess it's related to some optimizations whether to draw shadows or not?

The bug number is 708 853 339.