Deepslate transition doesn't line up across old and new chunks

Bedrock in old chunks is changed to deepslate, this means that the transition between deepslate and stone starts at y=4 and ends at y=0. That is not the case for 1.18 chunks. The transition starts at y=-1 and ends at y=-8. This means there's a noticeable border in the deepslate layout.

Can be reproduced in any world that was created before 1.18