Creating a new world with the "Caves" world generation option and setting the biome to "Plains" (might affect other biomes) generates a normal world. Simple. Going to the top of the world gen, however, shows that water lakes generate after the bedrock. This causes the game to make a lake that removes bedrock on the ceiling.
MC-215013
lake-generation-breaks-bedrock
Resolved
Duplicate
0
This appears to be a duplicate of MC-129235. which hasn't yet been resolved. If you have any additional information to provide regarding this issue, feel free to comment on the parent ticket. If you feel that this issue is affecting you, feel free to vote for the duplicated ticket, to give Mojang a basic idea of how many people are impacted by the problem. Just to further inform you, this will not determine how quickly the bug gets handled or fixed.