How to reproduce:

1. create a new image
2. add a layer for the environment map, e.g. Solid Noise mapped to a golden gradient
3. add a layer for the bumpmap, e.g. blurred what text on a black background
4. add some layers to play on, e.g. white, black and transparent
5. Use Lighting effects with the following settings (not all of them might be
relevant):

- transparent background
- high quality preview
- one directional light
- bumpmap with the layer from step 3
- environment map with the layer from step 2

6. update the preview if needed

For some layers, this will already show the problem.

7. Apply the plug-in

There are different possible results, the most common is a colored streak behind
the letters of the bumpmap. I'll attach an image that shows the problem.