Server doesn't generate amplified / large biome worlds

What I expected to happen was...:

The server should've generated an amplified world with level-type=amplified set.

What actually happened was...:

It generates a default world instead.

Steps to Reproduce:

1. Use the latest pre-release server .jar. (which can be found here)
2. In server.properties, set level-type to amplified (server changes "AMPLIFIED" or "Amplified" to all lower-case on startup).
3. Generate the world and behold a land strewn with defaultness.

Solutions I've tried:

• Setting server.properties to read-only to prevent the server from changing the level-type to lowercase.
• Generating the amplified world in singleplayer (which works, by the way) and copying the folder to the server (which doesn't work ).
• Messing around with the level.dat file to force the generator setting to amplified.
• Copying an old 1.15.2 amplified server world.

I'd like to note that none of the aforementioned solutions work.