Update: since the latest update of the kernel (2.6.31-12-generic -39) the oops/crash when the device is unplugged is gone but it's still not possible to detach the device and reconnect it later again. The option driver is not unloaded upon unplugging the device. And if I manually remove the option driver, it is not loaded anymore when the device is plugged in again. Even when I then load the driver manually, network-manager does not recognize/see the device again, thus I cannot use the modem.
Update: since the latest update of the kernel (2.6.31-12-generic -39) the oops/crash when the device is unplugged is gone but it's still not possible to detach the device and reconnect it later again. The option driver is not unloaded upon unplugging the device. And if I manually remove the option driver, it is not loaded anymore when the device is plugged in again. Even when I then load the driver manually, network-manager does not recognize/see the device again, thus I cannot use the modem.