Lava ocean changes world

When I create a custom world with lava ocean set to 'yes', it not just changes all the water into lava, but also other blocks are altered.
More specific:
I created a custom world with all values to default and seed 5397961323870334256. Then I go to coordinate 124 28 236. There I see a dead end cave. (picture 1)
Now I create another custom world with the same seed and also all default values except 'Lava Oceans' which is turned to 'Yes'. Now, when I go to the same coordinate I see the same cave, but now there is a small opening in the end. (picture 2) Through this opening I enter a new cave which shows the bottom of the ocean and lava floating in the air. (picture 3)
This same effect I saw in most of my other games with lava oceans turned to 'Yes'.