It’s because the API Keys are created from the OnRegistered AuthEvent whilst the users created from the Admin Users API only fire the OnCreated event, I’ve updated it so that it also executes the OnRegistered events in this commit which is enabled by default, and can be disabled with:
Plugins.Add(new AdminUsersFeature {
ExecuteOnRegisteredEventsForCreatedUsers = false
});
This change is available from v5.11.1 that’s now available on MyGet.