Why does this keep happening
It’s seamless, I used one cube and didn’t detach anything, and light still manages to escape through the corners.
What the fuck, Cinema 4D
Currently got this problem in 3ds max as well 
are you using vray by any chance?
thought this was going to be a thread about C4D R14 having a new sculpting feature
apparently not.
I don’t really see what could be going wrong here, its very weird.
Fixed it, I guess. Clicking on the light object, going to the shadow tab, and raising the density above 100% seemed to fix the problem.