Please describe the problem:
When you use the Lightning Effects plug-in (Filters -> Light Effects ->
Lightening Effects) with the Bump Mapping and Environment Mapping options, and
then choose the Transparent Background option in the Options tab, the background
of the rendered image will not be transparent. Instead it will be a semi
transparent blue-ish haze, and depending on the location of the light source
some or a lot of red horizontal lines will be visible in the image.

Steps to reproduce:
1. On an empty image right click and select "Filters -> Light Effects ->
Lightening Effects"
2. Activate Environment Mapping and select an image as environment map
3. Activate Bump Mapping and select a bump map image (should be grayscale)
4. In the Options tab, select "Transparent Background".
5. Render the image


Actual results:
The expected transparent background will be a semi transparent blue-ish haze,
and depending on the location of the light source, some or a lot of red
horizontal lines will be visible in the image.

Expected results:
The background is transparent.

Does this happen every time?
Yes, it does.

Other information:
Happens with the Windows build of Gimp 2.2.6.
Doesn't occur on the 1.2 version, which I have running on my Linux box.