Yep, not a big problem since I enjoyed the game, and the fact they've already replied to my plea on the bug thread may put the right attention on this ^_^
Thanks for the comment and nice piloting skill there! First time I got unscatched out of this stage was with the shotgun, then I tried your same loadout and as much as possible same conditions.
With no result...
So I came out with the idea that was the difference in the version of the game, do you think if I start a new playthru I could have a chance?

@Geno yeah kinda annoying, I posted in the bug thread that it might be restricted to the very first mission you play when you start up the gane. Also read your post and the dev's, hopefully you'll get it!

I did the same but didn't unlock the achievement, both waiting for the crab to come closer, and killing almost in water.