Ok, that hint helped. The problem is, that anacron does not run on battery by default (see Debian Bug report logs - #666390 anacron: change default ANACRON_RUN_ON_BATTERY_POWER to yes). As my laptop always runs on battery, anacron never runs.
What I do not understand is why it worked with my previous laptop, which was running wheezy. In the mentioned bug report it is said that anacron has always been configured to not run on battery. Jürgen
