"Lol, it was actually less than an hour, more like 10 minutes. I read the thread, went for a smoke, had an idea for what's causing it from the youtube video tested it out unmodified to duplicate the bug (by making the flashbang not explode for 20 seconds so i could get into position), went 'hmmm..', made the change to attempt to fix it, went in and tested again, no flash in tunnel. but i can still be flashed under normal circumstance.
In a nutshell.. that's my process for anything. Cigarette absolutely required."