Without lightmapping my scene works perfectly fine. Every light casts shadows on every other object.
After lightmapping the lights and shadows on static meshes are baked, thats okay so far. but the dynamic objects (which get lit dynamically) just casts shadows on other dynamic (therefore not lightmapped) objects, but not on the floor, which is lightmapped.
Every light in the scene has been set to lightmap mode = auto.
I may be wrong, but I don’t believe that the Single Lightmap mode allows for dynamic shadows.
I think that the idea behind SLMs is that you are probably going to use it for performance issues (because, if you weren’t, than Dual LM would be chosen, given that it has a prettier effect), and you want to tatoo the most information you can in an image so it doesn’t have to process in realtine. Dynamic elements used in SLM scenes probably shouldn’t realtime shadows (or would have a blob-shadow plane under them).
I’m searching for something similar myself: I want to have a single set of lightmaps for indirect lighting and ambient occlusion while keeping dynamic shadows so a single directional light can take the whole scene without losing prettiness, but I think that SLM rendering isn’t the way.
In Forward Rendering this is possible by using a single Directional Light in Auto mode.
Only one Directional light can cast shadows in Forward Rendering. You might use additional lights in Auto or Bake-only modes for baking the shadows in the lightmap (these won’t cast realtime shadows).
In Deferred Lighting you need to use an additional light in Realtime-only mode. This light will be combined with the already baked lights and shadows.