I think now I understand why this mode rendered black:

the shader, ist seems, doesnt use the geometrie for the edge, but the surface angle/normal. So its basically similar to a (smooth) step function on a normal shader with some fresnel or egde blend.

WHen you have bump, the pixel that in the "edge" angle are tinted with the outline color.

This is different to the comic book look that you can have in the editor.

Not sure if this is true, but thats my theorie about it - so it isnt really an error of the program, it just does slightly different things than you'd expect.

So you could make your own toon shader easily, that wokrs the same way I guess.