I think that happened when you chose to fire more than one torpedo at a target, remember in SH3 you could fire a single fish or 2>3>4 at one time then if you hit "Q" all the doors for the fish selected would open. I suspect its the same for SH4 at the Attack map....Not been there yet though still familiarizing myself of the lay-out/control/views.....I must say ONCE you get over the non AA and the jaggies it really is a wonderful graphic display of ships/subs/islands/trees everything is really top notch.
One bug i have found the "Next Target" key sometimes puts you in Mid air floating over a space of water with no target in view.
Deep six