legacy-only plugin does not load in Xenial

After installing network-manager-ssh package in 16.04 LTS, nothing new appears in the Add Connection dialog box, but I do get this message in the system logs:

Jun 03 09:58:40 sa1 gnome-session[27861]: ** Message: vpn: (ssh,/etc/NetworkManager/VPN/nm-ssh-service.name) cannot load legacy-only plugin

(FWIW, the same bug affects -ssh, -openconnect, -iodine, and -strongswan plugins; only OpenVPN, PPTP and VPNC are available.)

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: network-manager-ssh 0.9.4-1
ProcVersionSignature: Ubuntu 4.4.0-22.40-generic 4.4.8
Uname: Linux 4.4.0-22-generic x86_64
NonfreeKernelModules: nvidia_uvm nvidia
ApportVersion: 2.20.1-0ubuntu2.1
Architecture: amd64
Date: Fri Jun 3 10:07:38 2016
InstallationDate: Installed on 2016-05-28 (6 days ago)
InstallationMedia: Ubuntu 16.04 LTS "Xenial Xerus" - Release amd64 (20160420.1)
ProcEnviron:
 LANGUAGE=en_CA:en
 TERM=xterm-256color
 PATH=(custom, no user)
 LANG=en_CA.UTF-8
 SHELL=/bin/bash
SourcePackage: network-manager-ssh
UpgradeStatus: No upgrade log present (probably fresh install)