Unattended-upgrades do not seem to be able to restart services

[Jesper Dybdal <jd-debian@dybdal.dk>]

I am running up-to-date Jessie (8.5) with unattended-upgrades to provide
security upgrades.  But it seems that its attempts to restart services
fail.

Early this morning unattended-upgrades upgraded "libexpat1".

At the end of unattended-upgrades-dpkg.log, I see:

>Services to be restarted:
>Skipping dbus.service...
>systemctl restart apache2.service cron.service
>Log ended: 2016-06-08  04:36:36

However, apache2 and cron have not been restarted - they've been running
since June 5:

>root       622  0.0  0.0  27504  2860 ?        Ss   Jun05   0:00 /usr/sbin/cron -f
>root       748  0.0  0.1  80220  4928 ?        Ss   Jun05   0:02 /usr/sbin/apache2 -k start
>www-data   751  0.0  0.1 828208  5908 ?        Sl   Jun05   0:13 /usr/sbin/apache2 -k start
>www-data   752  0.0  0.1 500520  4688 ?        Sl   Jun05   0:13 /usr/sbin/apache2 -k start

If I manually execute the exact same systemctl command that
unattended-upgrades said that it used, it works fine:

# systemctl restart apache2.service cron.service

Now they have actually been restarted:
>root     27126  0.0  0.0  27504  2856 ?        Ss   22:04   0:00 /usr/sbin/cron -f
>root     27162  0.0  0.1  80220  5020 ?        Ss   22:04   0:00 /usr/sbin/apache2 -k start
>www-data 27165  0.0  0.1 369368  4452 ?        Sl   22:04   0:00 /usr/sbin/apache2 -k start
>www-data 27166  0.0  0.1 369368  4452 ?        Sl   22:04   0:00 /usr/sbin/apache2 -k start

I can find nothing in the logs about problems at that time (2016-06-08
04:36).

Can someone tell me what I've done wrong?
-- 
Jesper Dybdal, Denmark.
http://www.dybdal.dk (in Danish).