The only codes I used:

Try:

Try a new level without the shader and see if stencils show up, that might give you a comparative and from there you can determine what the cause may be for the current problems

Another factor to check out, is the model closed off? Important as a model with big holes will either display strange artifacts.

all meshs are closed..
With shadow_stencil before level initial, no shadow is shown..
The stencil isn´t shown without the shader, too

ok.. i made the sunlight off.. but still no shadow... *going crazy*

Maybe there's something in your code that disables the shadow??

I don't think so...
I only activate CAST in the light action, and shadows in the models action
No code wich disables the shadow functions..

It may be a dumb, or already answered question but

Is there any shader on the floor? That may be a problem...

No shaders on the floor or terrain

I tried it with a new script...
Just a ball with SHADOW flag, inside a cube, one dynamic light with CAST flag, and shadow stencil on 0,1 and 2
First gives no shadow (or it is to small to see)
The 1 & 2 are the blurred blob again...

Maybe you are using a graphics card that does not support stencil
But to be serious, the error must be in your code or your hardware(settings).
Maybe you set up some strange behaviour in your grahpics card's control panel!?