I am using 12.04. Since I use NM there is no way to connect to ADSL using wifi so I use PPPOE:

-Connect to wireless first (no it is not possible to connect to adsl on the modem/router, it is locked by the monolithic Chinese phone company)
-connect to internet with PPPOE (this took a long time to figure out but works fine now)
-connect to any VPN, PPTP, Ipsec, whatever, in NM and logs says connected. Result is PPPOE connection killed and no VPN.
-If use wired connection no problem, but is frustrating and inconvenient.

There must be a way to make it work. At this stage of Ubuntu development it should be a non-issue. Been using since Dapper, but every time get a workaround for something a new issue like this pops up. Buying a router is not an option since I use this setup at multiple locations and can't haul a router around with me.

Any help will be greatly appreciated!