The bug

I quickly tested by getting the vanilla server to convert an old banned-players.txt file to the new format because it calls this constructor.

simon8162|2016-01-01 12:00:00 GMT|admin|2018-01-01 12:00:00 GMT|reason

[
    {
        "uuid": "48708698-b1b1-43f2-908d-5383bbaa27bb",
        "name": "simon8162",
        "created": "2018-01-01 12:00:00 +0000",
        "source": "admin",
        "expires": "2018-01-01 12:00:00 +0000",
        "reason": "reason"
    }
]

"created" should be 2016-01-01 12:00:00 +0000 but is instead 2018-01-01 12:00:00 +0000

Code analysis

Source: https://github.com/SpongePowered/SpongeCommon/issues/1129
Faulty constructor: net.minecraft.server.management.UserListBansEntry.UserListBansEntry(GameProfile, Date, String, Date, String)