Comment 12 for bug 824147

I'm also affected by this bug. I replaced the line with

exec ltrace /usr/sbin/usb_modeswitch_dispatcher "$@" >/tmp/ltrace-$(date).txt 2>&1 &

to avoid name clashes, and, as Mathieu observed, the process exited normally (meaning that the usb modem got switched, modemmanager recognized it, and network-manager was able to use it). I'm attaching the last trace file for you to see, although now I'm not sure if it's useful or not.