ACLs are not correctly inherited

This bug is reported upstream and Ubuntu needs just a new package from the fixed version.
http://bugs.proftpd.org/show_bug.cgi?id=4303

The defaut ACLs of a parent directory are not correctly replicated on created
children. Actually, the mask is not correct.

user:k:rwx #effective:r-x

root@kls2:~# dpkg -l|grep proftp
ii proftpd-basic 1.3.5a-1ubuntu2
                amd64 Versatile, virtual-hosting FTP daemon - binaries

root@kls2:~# proftpd -v
ProFTPD Version 1.3.5a

root@kls2:/etc/proftpd# grep -ri acl *
modules.conf:ModuleControlsACLs insmod,rmmod allow user root
modules.conf:ModuleControlsACLs lsmod allow user *
modules.conf:LoadModule mod_facl.c

root@kls2:/etc/proftpd# grep modules.conf * -ri
proftpd.conf:Include /etc/proftpd/modules.conf

root@kls2:~# getfacl /home/workgroups/
getfacl: Removing leading '/' from absolute path names
# file: home/workgroups/
# owner: root
# group: root
user::rwx
user:k:rwx
group::r-x
group:vnstat:rwx
mask::rwx
other::r-x
default:user::rwx
default:user:k:rwx
default:group::r-x
default:group:vnstat:rwx
default:mask::rwx
default:other::r-x

root@kls2:~# getfacl /home/workgroups/New/
getfacl: Removing leading '/' from absolute path names
# file: home/workgroups/New/
# owner: k
# group: k
user::rwx
user:k:rwx #effective:r-x
group::r-x
group:vnstat:rwx #effective:r-x
mask::r-x <= the mask has switched from "rwx" to "r-x" !?
other::r-x
default:user::rwx
default:user:k:rwx
default:group::r-x
default:group:vnstat:rwx
default:mask::rwx
default:other::r-x
---
ApportVersion: 2.20.1-0ubuntu2.10
Architecture: amd64
DistroRelease: Ubuntu 16.04
InstallationDate: Installed on 2017-05-22 (91 days ago)
InstallationMedia: EOLE 2.6.1 "Xenial Xerus" - Beta amd64 (20170522)
Package: proftpd-basic 1.3.5a-1build1
PackageArchitecture: amd64
ProcVersionSignature: Ubuntu 4.4.0-87.110-generic 4.4.73
Tags: xenial
Uname: Linux 4.4.0-87-generic x86_64
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups:

_MarkForUpload: True
modified.conffile..etc.pam.d.proftpd:
 #%PAM-1.0
 auth sufficient /lib/security/pam_cas.so -sftp://192.168.0.26 -f/etc/pam_cas.conf
 auth sufficient pam_ldap.so
 @include login
mtime.conffile..etc.pam.d.proftpd: 2017-07-21T22:08:01.730215