Well, this tilt effect did go away after I reloaded the game (
)
HOWEVER, I noted something else interesting. These new Walruses in this mod must be thick as flies - when I loaded back into my saved game I was submerged in the eastern approaches to the Channel (and had been since just before dawn), so I popped up to the surface just to check the horizon for tilt (after scanning the area with my observation scope to make sure things were clear). I popped up to the bridge, confirmed that the horizon tilt was in fact gone, and then dove again immediately. On my way down, I was bombed by a Walrus! I had been on the surface less than a minute - amazing that he could have spotted me and gotten off a bombing run so quickly! Fortunately, he was a bad shot and missed me, though I was gonna go back to my previous saved game anyway - I play DID but I don't count troubleshooting tests for stuff like this and I would never have surfaced there at 9 in the morning to be spotted by planes if it weren't for that wierd horizon tilting thing anyway.