In my simple test case it worked (after showing twice the same image when both were rendering to the same rendertarget). Did you swap the rendertarget also in the material (e.g. using two different materials) and the material then in the widget (for testing I created two rendertargets, materials and widgets)?
Ahh nope. I just duplicated the render target actor. I will try swapping the material as well. Thanks a lot for the tips. I will let you know in a moment!