[Samba] Samba4 with Posix ACL's

[steve]

Hi everyone

I'm setting up a report writing system for a school. All teachers need 
rw access to the reports which are in a folder of the same name. 
Teachers are in a group called teachers and there is a share called reports:

[reports]
	path = /data/reports
	read only = No
	create mask = 0770

/data/reports has a Posix ACL:

  getfacl /data/reports
getfacl: Removing leading '/' from absolute path names
# file: data/reports
# owner: root
# group: teachers
# flags: -s-
user::rwx
group::r-x
other::---
default:user::rwx
default:group::rwx
default:other::---

and ls gives:
  drwxr-s---+ 9 root teachers  4096 Apr 15 11:47 reports

Under XP, everything works as expected. Only teachers can enter the 
share and any report created becomes group rw. Perfect.

In Windows 7, no one can enter. Clicking on the security tab we can see 
the teachers group listed (so it must know something about group 
ownership or the ACL or both) but nothing is ticked apart from 'special 
permissions'. Administrator has to select read and write before the 
teachers can enter. There is then a warning about setting permissions at 
the root of the share.

What have I done wrong?
Does w7 under Samba4 understand Posix ACL and group rw stuff?
Cheers,
Steve