no connection after booting with modem plugged in

I have a USB modem Huawei E3251 (DC-HSPA+ USB modem).
It is a 3G device, although not quite a usual one: In the NetworkManager applet it shows itself as an ethernet or wired connection.

How to reproduce the bug:

1.) Have a PC (with ubuntu 14.04 LTS) which is first turned off. Plug the modem into one of its USB ports.

2.) Turn on the PC and boot the ubuntu. (It logs me automatically.) Unfortunatelly, after the boot the NetworkManager is completely ignorant of the modem and networking does not work.

If I want to start networking anyway, I have to physically unplug the modem and plug it again. This is pretty annoying.

BTW, if the networking is finally working and I just restart the machine, the networking works after the reboot. It even connects me automatically.

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: modemmanager 1.0.0-2ubuntu1
ProcVersionSignature: Ubuntu 3.13.0-24.47-generic 3.13.9
Uname: Linux 3.13.0-24-generic x86_64
ApportVersion: 2.14.1-0ubuntu3
Architecture: amd64
Date: Sat May 10 09:57:10 2014
InstallationDate: Installed on 2014-01-31 (98 days ago)
InstallationMedia: Ubuntu 14.04 LTS "Trusty Tahr" - Alpha amd64 (20140130)
SourcePackage: modemmanager
UpgradeStatus: No upgrade log present (probably fresh install)