Having two network interfaces causes internet traffic to cease on boot

[penalvch]

What is expected to happen in a new Vivid virtualbox guest from a Trusty host is one clicks in vbox File > Preferences > Network > Host-only Networks > click plus icon to Add host-only network > IPv4 Address: 192.168.56.1 > IPv4 Network Mask: 255.255.255.0 > IPv6 Address: fe80:0000:0000:0000:0800:27ff:fe00:0000 > IPv6 Network Mask Length: 64 > tab DHCP Server > uncheck Enable Server > OK > highlight Vivid guest > Settings > Network > tab Adapter 1 > Attached to: NAT (leave all other settings as default) > tab Adapter 2 > check Enable Network Adapter > Attached to: Host-only Adapter (leave defaults) > Check Enable Network Adapter > OK.

Start the Vivd guest and login > top right of screen secondary click Network Manager icon in the taskbar > Settings... > highlight WIred Connection 1 > Edit > tab IPv4 Settings > button Add > Address 192.168.56.4 > Netmask 255.255.255.0 > Gateway 192.168.56.1 > Save > restart and NAT traffic through Wired Connection 1 works.

What happens instead is it doesn't. This also happens if one saves the machine state, and resumes it. Things I've tested:
- This didn't happen in 12.04.5 with the same kernel as in Vivid, so this is a regression from at least Precise.
- In Vivid I've tested kernel 3.2, and 3.19-rc1 and the same problem was reproducible, so this isn't a linux kernel issue.
- I tried upgrading the version of virtualbox from default 4.3.10 to 4.3.20, no change.

WORKAROUND: Click Network Manager icon in the taskbar > click Wired connection 2, which will disable it. Then, click it again to re-enable. This will allow for both the NAT traffic to begin working again, and the host-only traffic will work.

ProblemType: Bug
DistroRelease: Ubuntu 15.04
Package: network-manager 0.9.8.8-0ubuntu34
ProcVersionSignature: Ubuntu 3.16.0-28.38-generic 3.16.7-ckt1
Uname: Linux 3.16.0-28-generic x86_64
ApportVersion: 2.15.1-0ubuntu1
Architecture: amd64
CurrentDesktop: Unity
Date: Sun Dec 28 03:48:31 2014
IfupdownConfig:
 # interfaces(5) file used by ifup(8) and ifdown(8)
 auto lo
 iface lo inet loopback
InstallationDate: Installed on 2014-12-14 (14 days ago)
InstallationMedia: Ubuntu 15.04 "Vivid Vervet" - Alpha amd64 (20141213)
IpRoute:
 default via 10.0.2.2 dev eth0 proto static
 10.0.2.0/24 dev eth0 proto kernel scope link src 10.0.2.15 metric 1
IwConfig:
 eth0 no wireless extensions.

 eth1 no wireless extensions.

 lo no wireless extensions.
NetworkManager.state:
 [main]
 NetworkingEnabled=true
 WirelessEnabled=true
 WWANEnabled=true
 WimaxEnabled=true
RfKill:

SourcePackage: network-manager
UpgradeStatus: No upgrade log present (probably fresh install)
mtime.conffile..etc.NetworkManager.NetworkManager.conf: 2014-12-26T05:59:48.680074
nmcli-con:
 NAME UUID TYPE TIMESTAMP TIMESTAMP-REAL AUTOCONNECT READONLY DBUS-PATH
 Wired connection 1 c877b163-ed83-464c-92b2-e56fdeefc0b4 802-3-ethernet 1419760097 Sun 28 Dec 2014 03:48:17 AM CST yes no /org/freedesktop/NetworkManager/Settings/1
 Wired connection 2 a12f34d9-04d3-44d3-aa0d-7bbbbeb90c3f 802-3-ethernet 1419663760 Sat 27 Dec 2014 01:02:40 AM CST yes no /org/freedesktop/NetworkManager/Settings/0
nmcli-dev:
 DEVICE TYPE STATE DBUS-PATH
 eth1 802-3-ethernet disconnected /org/freedesktop/NetworkManager/Devices/1
 eth0 802-3-ethernet connected /org/freedesktop/NetworkManager/Devices/0
nmcli-nm:
 RUNNING VERSION STATE NET-ENABLED WIFI-HARDWARE WIFI WWAN-HARDWARE WWAN
 running 0.9.8.8 connected enabled enabled enabled enabled disabled