Because of This post I decided to try downgrading to 6.9.2 and the ACLs worked. I'm not sure what these mount options mean, but maybe they would explain why it works in 6.9.2 but not 6.10.3:
6.9.2 ACLs work:
root@nas:~# mount | grep /mnt/user
shfs on /mnt/user0 type fuse.shfs (rw,nosuid,nodev,noatime,allow_other)
shfs on /mnt/user type fuse.shfs (rw,nosuid,nodev,noatime,allow_other)
6.10.3 ACLs do not work:
root@nas:~# mount | grep /mnt/user
shfs on /mnt/user0 type fuse.shfs (rw,nosuid,nodev,noatime,user_id=0,group_id=0,default_permissions,allow_other)
shfs on /mnt/user type fuse.shfs (rw,nosuid,nodev,noatime,user_id=0,group_id=0,default_permissions,allow_other)
Should we get this post moved to bug reports?
E: I should not that sudo -u test was not working for testing permissions in 6.9.2, but the ACL worked correctly in my samba shares.