I see, but when I created the map in 0.16.51 I explicitly deactivated cliffs, so I don't understand why this setting was changed when I switched to 0.17, as now I have cliffs

Hello there.
So, I was playing in 0.16.51 with my friend and in the map we generated, I turned off Cliffs. We played for 100+ hours, and then took a pause, as we were waiting for 0.17. When it came out, we waited a little more before continuing our game, until 0.17.4 came out, then we started ...