Luxrender - black background after exporting into EXR

I’m always getting black background after exporting render results into EXR image.
See attachments.

  • one is Lux screenshot.
  • second is screenshot from LightRoom (LuxRender (ok) -> OpenEXR -> FDRToolsBasic for 16bit TIFF (get black background) -> Adobe LightRoom (again, black background))

I’ve tried all possible combinations of “Alpha premultiply”, but again and again I’m getting black background. Lighting done by simple hemisphere. Same results for Sun&Sky.