Created attachment 170826 [details]
ifconfig and route tables log

Overview:
My ISP provides metropolitan area Ethernet network (eth0) and PPPoE connection for access to Internet (ppp0). However, NetworkManager (NM) disconnects eth0 while establishing ppp0 (log with ifconfig and route tables is attached).
I believe that this bug is caused by assumption that PPPoE and Ethernet can not run simultaneously without conflicts.  Or probably by assumption that one network may work only if some other are on/off.  However, I can setup these networks (with system-config-network tool) to work simultaneously.
I think NM should be able to turn on/off each network separately and independently. Right now NM implements something like switching between networks. I'm sure, this is a wrong way. Actually it complicates NM setup and also its development and bugfixing. I have looked at buglist, I have found some bugs which are resulted by this inconvenience.
Why don't to let the user to decide which network he like to run or to turn off? It will not violate your Design Goals. If something goes wrong (routes conflicts, lost connection, etc.), NM always may notify the user.

Steps to reproduce:
1) Setup Ethernet and PPPoE connections (you should have a machine connected to such networks)
2) Run Ethernet interface
3) Run PPPoE connection

Actual Results:
If you open nm-applet menu (click left button on tray icon) you will see that the Ethernet connection now is inactive.

Expected Results:
Ethernet should be on.

Build Date & Platform:
Build from master branch Wed Sep 22, 9:00 GMT, Fedora 13.