No light sources but object illuminated My set has no light sources and no environment maps, resulting in black background - however, the objects are still illuminated. Have I enabled some obscure setting by mistake?

PS. This is in Cycles. When switched to Eevee, everything is back as expected.
Your problem is that you've enabled Ambient Occlusion. Ambient Occlusion is a fake light that was mostly used in Blender Render to improve the shadows. I'm not sure it's still very useful with 2.8 except maybe for some effects like baking shadows...

Vader explanation here. Manual explanation here.