I've converted world from 1.12.2 to 1.13-pre3, and teleported to 0 64 0 (I've never been on these cords), and I see this:
Related issues
Attachments
Comments

[media][media]

Was it a superflat world originally? Can you provide the seed?

It was Tunnelers’ Dream with stone lvl changed to 52
Confirmed in 1.13-pre3. I'm unable to reproduce in 1.13-pre5 because of MC-132375.
I'm not able to reproduce anymore in 1.13-pre9.