Websocket Configuration results in "Error in poll: Interrupted system call."

[Grossmann200]

Hi,
so far, mqtt runs fine on my Raspberry Pi.
Now, I wanted to use the websocket and added in /etc/mosquitto/conf.d the file websocket.conf with following content:

listener 1883
listener 9001
protocol websockets


After restarting the mqtt-broker, it is not runnging. The mqtt-log file provides the following:

1479474013: mosquitto version 1.4.10 (build date Thu, 25 Aug 2016 10:12:09 +0100) starting
1479474013: Config loaded from /etc/mosquitto/mosquitto.conf.
1479474013: Opening ipv4 listen socket on port 1883.
1479474013: Opening ipv6 listen socket on port 1883.
1479474059: Error in poll: Interrupted system call.
1479474059: mosquitto version 1.4.10 terminating

Any idea, what I am doing wrong.
I used the mqtt-broker from following repository:
# sudo curl -O http://repo.mosquitto.org/debian/mosquitto-wheezy.list