Comment 5 for bug 490194

I experienced the same issue under Ubuntu 13.04 with a prototype research device using a Bluetooth SPP module over /dev/rfcomm (like Roland already pointed out) and this issue probably affects lots of people working with self-built Bluetooth or cable bound serial port devices. This is a very bad and non-acceptable behavior of modemmanager for the following reasons:

1. Things break that used to work before an distribution update. In the past, unfortunately I do not know the exact version but 11.x should have worked, things worked. Maybe modemmanager was not probing devices automatically or was not activated/installed by default. From a user perspective, there is no easy way to find out why things don't work as expected anymore. I, for example, had to inspect the memory holding the incoming bytes on my microcontroller to realize that more bytes arrive than my application is actually sending. It took me quite a while and it was really annoying.

2. Devices might behave unusual from one day to the next after an update, because they receive bytes they do not expect. In the best case, the devices do not work at all, in the worst case they behave oddly and might even get damaged or cause damage (robots, control devices... who knows what's out there)

From what I read in other bug reports, the developers of modemmanager favor a blacklist of devices not to probe as the solution to this issue. I strongly disagree with this solution because it is not working for all the prototype devices and relies on the idea that every problem has to occur once and annoy somebody once before it is solved.