Board Thread:Bug Reports/@comment-25565811-20160917181834/@comment-27516710-20160920201736

Yes, imagine the ground is solid there, fences generate, then caves or other parts are then generated - removing the ground that was under the fence. The algorithm only affects normal ground items - dirt, grass, stone, ores - that's why the fences are not removed and why vineyards can occur over deep ravines.