And that's the crux of the problem - a "design feature" is actually a "design fault". Irrespective of which trigger is pulled first (either deliberately or accidentally) a double rifle shouldn't double discharge for the pull of a single trigger.

I've seen a copy of a Merkel operators manual and it states firing the front trigger first and within 16 seconds firing the rear to ensure proper regulation of the shots. It doesn't mention risk of double discharge if the wrong firing sequence is made - to ignore mention of this fact is negligent. I don't know if any subsequent manuals were revised accordingly but then doing so would just highlight a known design fault and negligence anyway. I understand that the more recent Merkels do have additional precautions to prevent doubling from happening (separate interceptor on each trigger mechanism?).