No idea about why you can't get down past about 450 feet - does sound strange.
However, the "rebound" effect is probably coming from the fact that (IIRC) the "crash dive" command is preset in some .cfg file or somewhere to tell the boat to go to a certain depth (like maybe 120 feet, or 150 feet, or whatever) - thus, if you issue the command while surfaced or even at periscope depth (which I suspect is where the game expects you to be when you issue that command), it will take you down to that pre-set depth. However, if for some odd reason you issue that order while you're already below the pre-set crash-dive depth, the game will probably try to take you to that pre-set depth anyway, which of course would mean that it would be taking you up, not further down, in that case. No idea why you would get damage while going up that way, unless maybe it's just the delayed domino effect and your boat was just reacting (in a delayed manner) to the fact that maybe you had been below crush depth for a while.
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