Hey, sorry for the enigmatic title but I couldn't find a better way to describe it.

Here's my problem: where does this shadow of a cube come from???

If you look at the file, there is only one cube, and one sphere. I deactivated the render for the light and the camera, and the only shadow caster is the sphere (geo2). So why is there a cube shadow when the light goes behind the sphere? To be sure, I also tried replace the cube by a sphere, and the shadow cube is still there... I also of course looked in my two geos to see if there is a remaining box somewhere.

So for now still no clue about where this shadow comes from...

Any idea? Thanks in advance!