NetworkManager 0.9 has changed a lot of stuff. Before NM 0.9, there are user connections and system connections. Ifnet plug-in is made to only take charge of system connections. But after NM 0.9, all connections become system connections and ifnet tries to manage all of them. Then some bad things might happen. The problem is reported by David Narvaez and he helped a lot on it. Bug #392409 is also caused by the problem. This is fixed in networkmanager-0.9.2.0-r2: if a user does not check “available to all users”, ifnet will not handle the connection any more and the default plug-in “keyfile” will do the job.
Another important change is that ifnet now supports openrc style. As bash arrays are not allowed by openrc, ifnet caused Bug #369711. After networkmanager-0.9.2.0-r2, ifnet can read both the old baselayout style (with bash arrays) and openrc style (without bash arrays), but it only writes to /etc/conf.d/net with openrc style.