starts "apt-get -s upgrade" everytime it starts, but doesn't stop them when it exits

Version: 4.37-1

When starting and exiting byobu several times in a row (e.g. for testing some stuff), for each start there seems a "apt-get -s -o Debug::NoLocking=true upgrade" process running, clogging up the system more and more with every byobu start.

I'd expect that

a) just one such process is running at a time, especially if no more than one byobu was running at a time,
b) the process gets killed if byobu is stopped

-- System Information:
Debian Release: wheezy/sid
  APT prefers unstable
  APT policy: (990, 'unstable'), (900, 'testing'), (600, 'stable'), (400, 'oldstable'), (110, 'experimental')
Architecture: i386 (i686)

Kernel: Linux 3.1.0-rc7-686-pae (SMP w/1 CPU core)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash

Versions of packages byobu depends on:
ii debconf [debconf-2.0] 1.5.41
ii gettext-base 0.18.1.1-5
ii perl 5.12.4-6
ii python 2.7.2-9
ii python-newt 0.52.11-2.1
ii screen 4.1.0~20110819git450e8f3-1

byobu recommends no packages.

Versions of packages byobu suggests:
pn apport <none>
pn lsb-release 3.2-28
pn po-debconf 1.0.16+nmu1
pn tmux 1.5-2
pn update-notifier-common <none>
pn vim <none>
pn w3m <none>

-- debconf information:
  byobu/launch-by-default: false