dash shell leaves zombies upon SIGTERM

Repro is trivial, just follow these steps:

$ /bin/dash -c 'sleep 2h' &
[1] 123304

$ ps -Af|grep sleep
user 123304 64999 0 14:28 pts/0 00:00:00 /bin/dash -c sleep 2h
user 123306 123304 0 14:28 pts/0 00:00:00 sleep 2h
user 124220 64999 0 14:28 pts/0 00:00:00 grep --color=auto sleep

$ kill 123304
[1]+ Terminated /bin/dash -c 'sleep 2h'

$ ps -Af|grep sleep
user 123306 1 0 14:28 pts/0 00:00:00 sleep 2h
user 124224 64999 0 14:29 pts/0 00:00:00 grep --color=auto sleep

ProblemType: Bug
DistroRelease: Ubuntu 15.10
Package: dash 0.5.7-4ubuntu2
ProcVersionSignature: Ubuntu 4.2.0-16.19-generic 4.2.3
Uname: Linux 4.2.0-16-generic x86_64
ApportVersion: 2.19.1-0ubuntu4
Architecture: amd64
CurrentDesktop: LXDE
Date: Thu Oct 29 14:19:43 2015
ExecutablePath: /bin/dash
InstallationDate: Installed on 2015-09-08 (50 days ago)
InstallationMedia: Lubuntu 15.04 "Vivid Vervet" - Release amd64 (20150422)
SourcePackage: dash
UpgradeStatus: No upgrade log present (probably fresh install)