Comment 3 for bug 1067337

I think this is the output when it happens:

modem-manager[7169]: <debug> [1350412098.663568] [mm-manager.c:690] supports_callback(): (tty/ttyUSB6): ignoring port unsupported by physical modem's plugin
modem-manager[7169]: <debug> [1350412098.663733] [mm-manager.c:298] check_export_modem(): (tty/ttyUSB8): outstanding support task prevents export of /sys/devices/pci0000:00/0000:00:1d.7/usb1/1-8
modem-manager[7169]: <debug> [1350412099.661949] [mm-qcdm-serial-port.c:196] debug_log(): (ttyUSB8): --> 7e 00 78 f0 7e
modem-manager[7169]: <debug> [1350412102.664499] [mm-serial-port.c:908] mm_serial_port_close(): (ttyUSB8) device open count is 0 (close)
modem-manager[7169]: <info> [1350412102.664663] [mm-serial-port.c:923] mm_serial_port_close(): (ttyUSB8) closing serial port...
modem-manager[7169]: <info> [1350412102.664828] [mm-serial-port.c:944] mm_serial_port_close(): (ttyUSB8) serial port closed
modem-manager[7169]: <debug> [1350412102.666134] [mm-manager.c:714] supports_callback(): (tty/ttyUSB8): plugin 0x8b4bae0 (Cinterion) existing 0x8b4bda0 (Sierra) info->best 0x8b4bda0 (Sierra)
**
ERROR:mm-manager.c:715:supports_callback: code should not be reached