[Samba] "map to guest = bad user" ignored in Samba 4?

[Sebastian Arcus]

I would like to migrate some of my Samba 3.x domains to Samba 4. Part of 
the functionality of the current system is allowing some Windows XP Pro 
computers, which are not joined to the domain, access to some public 
shares on the Samba server. I tried using "map to guest = bad user" with 
Samba 4 - but it appears to be completely ignored and the Windows XP 
machine keeps on prompting for username/password when trying to access 
the server share. Has this option been dropped in Samba 4? Is there 
another way to accomplish the same?

Otherwise my Samba 4 domain seems to be working fine - and the Windows 
XP Pro machines which are joined to it can access the share fine.

As a side note, I find it hard to figure out which smb.conf options are 
still available for Samba 4 and which are not. I've googled around and 
can't seem to find a wiki page or authoritative page.

I use Samba 4.1.0pre1

Here is my smb.conf


[global]
workgroup = MYDOMAIN
realm = mydomain.local
netbios name = MY-SERVER
server role = active directory domain controller
idmap_ldb:use rfc2307 = yes
map to guest = bad user

[netlogon]
path = /var/lib/samba/sysvol/mydomain.local/scripts
read only = No
public = Yes