When downloading and running the pre-release 8 server jar, the server claims it is a pre-release 7 jar, and won't allow pre-release 8 users to join.
how to repeat:
Use this link: https://launcher.mojang.com/v1/objects/1a8d87a8bc254721e75e27cf567ed11dba5cb91f/server.txt
Then run the server and the game
Try to join, will claim you are on the wrong client, also the log will claim that it is pre-release 7.
That's the server obfuscation mappings.
Use this link instead: https://launcher.mojang.com/v1/objects/051efe8853d00db6bef7f19324da25a465782376/server.jar