This mod is great, realistic, and that's what I particularly like in the game. Thanks to these more than magnificent landscapes, we have access to new opportunities to build, with mountains sometimes very close to the sea which are beautiful to see, and delightful to use. Thanks for this fantastic mod.
I noticed a problem which is that along lakes or seas there is water under continents, islands, even trees.
About the problem you describe, did you set the mapgen to singlenode at world creation? Water under continents makes me think about another mapgen interfering, and currently mapgen_rivers does not check for this.