I'm not sure that this is really a duplicate of bug 74142 - that other bug is about "generic" PPP support in NetworkManager, while this bug here is specifically about dial-on-demand support for a PPP-enabled NetworkManager (in more detail: usually PPP under Linux requires to manually run some command like "pon" to start the internet connection and something like "poff" to disconnect; Dial-on-Demand means that the system automatically makes a connection when it detects that you want to access a web site, and it automatically disconnects if you do not use the connection for a while).
So in my opinion this is not really a duplicate (also the upstream bug doesn't seem to mention Dial-on-Demand); but on the other hand I'm not familiar with Launchpad and what constitutes a duplicate here.
I'm not sure that this is really a duplicate of bug 74142 - that other bug is about "generic" PPP support in NetworkManager, while this bug here is specifically about dial-on-demand support for a PPP-enabled NetworkManager (in more detail: usually PPP under Linux requires to manually run some command like "pon" to start the internet connection and something like "poff" to disconnect; Dial-on-Demand means that the system automatically makes a connection when it detects that you want to access a web site, and it automatically disconnects if you do not use the connection for a while).
So in my opinion this is not really a duplicate (also the upstream bug doesn't seem to mention Dial-on-Demand); but on the other hand I'm not familiar with Launchpad and what constitutes a duplicate here.