This has now been fixed in Beta 0.24

Is the SF shader set to Off or Alpha Blended, in the blending settings?
Are you using deferred or forward rendering? (Check both the camera and the player settings)

It is, but there are so many parameters that you might want to tweak. It could be expanded into an entire "preview light source editor" for adding/removing lights, setting the light type, enabling/disabling shadows, changing color, position, saving presets, loading presets, and, the list goes on!

The question is rather; which are the priamry reasons you want other light setups in the preview, and how can it be minimised into as few controls as possible to keep it simple to use, while retaining the usefulness?

I do plan to add a way to rotate the light setup, but I'm not sure yet how to deal with the other parameters.

Hm, good point. There should be a way of disabling shadows per-shader rather than only having it per-object. Feel free to open a topic on the matter!

Cool, it's my fault then :)
It's fixed for the next version!

(The texture itself, not the node)

One more thing - was the texture marked as a normal map?

This has been fixed in Beta 0.24

I would have thought the transformation would keep the normalization, but I guess not :)