Comment 107 for bug 868034

If I may refer to my comment #85 - I had a look at the "working" and "nonworking" log of modem-manager and pointed out the obvious differences.

I strongly suspect that the newer version of MM is attempting to make use of the diagnostic port, which can give status information (like signal strength) even during a connection.
In this case though, it affects the modem in some bad way; I doubt the log will help much to pinpoint the underlying problem ...