Nintendo has responded to the issue of the Locked Red Door bug: It occurs if you backtrack after acquiring the Ice Beam.
So that's the thing that causes it, huh? Most sites I read online said the thing that triggers the bug is if you go back and save after beating the last boss prior to the locked doors, but I KNEW that wasn't the cause because I never did that and it was still locked for me.
I'm not paying to send an SD card to Japan so that Nintendo can fix this for me. Its just bullshit that they won't release a patch or something online to fix this problem. It sucks that I have to restart the game now and lose the 9 hours I invested in it, but at least NOW I know exactly what triggers the bug so I will be able to avoid it from happening the next time around. I've been stuck at that locked door for about two weeks now and I haven't played the game at all because I was hoping Nintendo would release a patch or something, but sadly now it looks obvious that they're not going to do that. I also didn't want to restart the game because I didn't know what the trigger for the bug was, but now that I do I guess I will restart.
But you know what? This is absolutely ridiculous for this to happen in ANY Metroid game. The Metroid series is supposed to be all about encouraging exploration and backtracking to pick up the powerups and unlock all the secrets. I can forgive many of the flaws with Other M, but this one is unacceptable. As soon as I finish this game I'm going to sell it so I can wash my hands of it. I never thought I would say that about any Metroid game, but this one has crossed the line, IMHO.