Agreed. The custom world setting was a godsend for mapmakers who wanted Minecraft generated terrain. If it won't be available for the 1.13 update, it'll be frustrating. Please, Mojang, reconsider this bug and get it fixed before the release!
They did fix the stairs to keep water from flowing out the back, so I do not see why they cannot fix this as well. And I did use the search function before posting. The search function did not pull up that issue. Thank you for your information, but it is unnecessary.
Bees are still disappearing and despawning in 1.18.1. The patch didn't fix it.