After plugging in a USB Huawei Mobile GSM modem (idVendor=12d1, idProduct=1003,
sold - among others - as "Fonic Surfstick" in Germany), it is not possible to
connect via broadband with this device. However, after restarting
NetworkManager, the connectin works fine. The bahaviour is similar to
https://bugzilla.redhat.com/show_bug.cgi?id=1230681 . 

How to reproduce:
1. Make sure NetworkManager and ModemManager are enabled and running
2. Create a NetworkManager connection for the Huawei Mobile
3. Reboot
4. Log in to a graphical desktip session (in my case: lxde)
5. Make sure the NetworkManager applet is running and working
6. Plug in the USB Huawei Mobile GSM modem
7. Unlock the SIM card if necessary
8. Try to connect with the Huawei Mobile

Error messages from journalctl:
Dez 30 22:10:02 probook NetworkManager[27645]: <info>  (ttyUSB1): Activation:
starting connection 'FONIC Surfstick' (d16f9a53-30ee-4f1c-8af1-2609ab4f2d15)
Dez 30 22:10:02 probook NetworkManager[27645]: <info>  (ttyUSB1): device state
change: disconnected -> prepare (reason 'none') [30 40 0]
Dez 30 22:10:02 probook NetworkManager[27645]: <warn>  (ttyUSB1): Failed to
connect 'FONIC Surfstick': Connection requested both IPv4 and IPv6 but
dual-stack addressing is unsupported by the modem.
Dez 30 22:10:02 probook NetworkManager[27645]: <info>  (ttyUSB1): device state
change: prepare -> failed (reason 'modem-init-failed') [40 120 28]

After restarting the NetworkManager service, the connection can be made
successfully. 

The error message about "IPv4 and IPv6" is misleading. I tried setting the
connection to IPv4 only and it did not work either (though the message changed
to "Connection requested IPv4 but IPv4 is unsuported by the modem.")