Haha, same thing kind of happened to me (with sabatoge and malfunctions enabled) and I paid the price.
I was cruising along with my TC at 512 and suddenly came across a destroyer leading a small convoy (my watch crew was a little late in notifying me).
Anyway I was pretty close so I ordered a crash dive. I heard the "ALARM!", etc., and went to the control room view to await the impending depth charges that I figured were coming.
Unfortunately it took me a while to realize that my speed had went to 0 even though the indicator was sitting at flank.
And then I got blasted by the destroyer's guns! And that was the end of me.....
Dang malfunctions/sabotage!
Dale