I have a scene with one light and a sphere with an texture. With the keys I can increase/decrease the scale (ISceneNode->setScale()). It works fine but when I let the sphere grow, it gets darker and when I let it shrink, it gets brighter. The effect is cleary noticable, if I scale from 0.5 to 1.5 for example the sphere changes its brightness from white to dark grey.
The normals are also scaled, this is ( ) normal behavior. But you can (and should for every dynamically lit and scaled mesh) set the material flag EMF_NORMALIZE_NORMALS to true and normals are automatically normalized again.