Dave, thanks, but moving the interpolation slider from 50 to 100 to 0 seems to not affect the rectangle problem if the box is unchecked.

I remember another post several weeks back, someone was complaining about their animation having gritty, jumpy I-L (in C2.1). Possibly related to what I'm seeing. Hope this is something Eovia is already working on.

On the plus side, with interpolation off increasing the photon count definitely helps the flickering I-L light level, so I'm very grateful for knowing about that.

Sorry for highjacking your thread! :-)