It's not a kernel bug or something. Must be something about NetworkManager.

Kernel: 3.5.1
DE: Cinnamon 1.4UP3

network-manager                        0.9.4.0-0ubuntu4.1
network-manager-gnome          0.9.4.1-0ubuntu2
network-manager-pptp              0.9.4.0-0ubuntu1

Bus 002 Device 005: ID 12d1:1404 Huawei Technologies Co., Ltd. 
Couldn't open device, some information will be missing
Device Descriptor:
  bLength                18
  bDescriptorType         1
  bcdUSB               2.00
  bDeviceClass            0 (Defined at Interface level)
  bDeviceSubClass         0 
  bDeviceProtocol         0 
  bMaxPacketSize0        64
  idVendor           0x12d1 Huawei Technologies Co., Ltd.
  idProduct          0x1404 
  bcdDevice            0.00
  iManufacturer           3 
  iProduct                2 
  iSerial                 0 
  bNumConfigurations      1



Syslog:

Aug 15 11:39:59 black NetworkManager[911]: <info> Activation (ttyUSB0) starting connection 'T-Mobile(Telekom) Vorgabe'
Aug 15 11:39:59 black NetworkManager[911]: <info> (ttyUSB0): device state change: disconnected -> prepare (reason 'none') [30 40 0]
Aug 15 11:39:59 black NetworkManager[911]: <info> Activation (ttyUSB0) Stage 1 of 5 (Device Prepare) scheduled...
Aug 15 11:39:59 black NetworkManager[911]: <info> Activation (ttyUSB0) Stage 1 of 5 (Device Prepare) started...
Aug 15 11:39:59 black NetworkManager[911]: <info> (ttyUSB0): device state change: prepare -> need-auth (reason 'none') [40 60 0]
Aug 15 11:39:59 black NetworkManager[911]: <info> Activation (ttyUSB0) Stage 1 of 5 (Device Prepare) complete.
Aug 15 11:39:59 black NetworkManager[911]: <info> Activation (ttyUSB0) Stage 1 of 5 (Device Prepare) scheduled...
Aug 15 11:39:59 black NetworkManager[911]: <info> Activation (ttyUSB0) Stage 1 of 5 (Device Prepare) started...
Aug 15 11:39:59 black NetworkManager[911]: <info> (ttyUSB0): device state change: need-auth -> prepare (reason 'none') [60 40 0]
Aug 15 11:39:59 black NetworkManager[911]: <info> Activation (ttyUSB0) Stage 1 of 5 (Device Prepare) complete.
Aug 15 11:39:59 black modem-manager[837]: <info>  (ttyUSB0) opening serial port...
Aug 15 11:39:59 black modem-manager[837]: <info>  Modem /org/freedesktop/ModemManager/Modems/0: state changed (disabled -> enabling)
Aug 15 11:40:00 black modem-manager[837]: <warn>  (ttyUSB0): failed to query SMS mode, assuming text mode
Aug 15 11:40:00 black modem-manager[837]: <warn>  (ttyUSB0): failed to enable USSD notifications.
Aug 15 11:40:00 black modem-manager[837]: <info>  Modem /org/freedesktop/ModemManager/Modems/0: state changed (enabling -> disabled)
Aug 15 11:40:00 black modem-manager[837]: <info>  (ttyUSB0) closing serial port...
Aug 15 11:40:00 black modem-manager[837]: <info>  (ttyUSB0) serial port closed
Aug 15 11:40:00 black NetworkManager[911]: <warn> GSM modem enable failed: (32) Failed to find a usable modem character set
Aug 15 11:40:00 black NetworkManager[911]: <info> (ttyUSB0): device state change: prepare -> failed (reason 'modem-init-failed') [40 120 28]
Aug 15 11:40:00 black NetworkManager[911]: <info> Marking connection 'T-Mobile(Telekom) Vorgabe' invalid.
Aug 15 11:40:00 black NetworkManager[911]: <warn> Activation (ttyUSB0) failed.
Aug 15 11:40:00 black NetworkManager[911]: <info> (ttyUSB0): device state change: failed -> disconnected (reason 'none') [120 30 0]
Aug 15 11:40:00 black NetworkManager[911]: <info> (ttyUSB0): deactivating device (reason 'none') [0]
Aug 15 11:40:00 black NetworkManager[911]: nm_system_iface_flush_routes: assertion `ifindex > 0' failed
Aug 15 11:40:00 black NetworkManager[911]: nm_system_iface_flush_addresses: assertion `ifindex > 0' failed