NetworkManager wired ethernet times out waiting for dhcp on 14.04 trusty tahr

I'm experiencing dhcp timeouts on 14.04 that I didn't experience in earlier releases (13.10 and 12.04 are in use in the office). Others in my office have similar complaints that "wired ethernet stops working in 14.04" which all equate to a dhcp timeout. When switching back to 13.10 dhcp works flawlessly.

network-manager 0.9.8.8-0ubuntu7 (the current version on trusty) contains the following changelog:
* debian/tests/nm: Bump DHCP timeouts from 15 to 20 seconds, something in
    the stack got even slower as it used to be.
  * debian/tests/nm: With the patch in 0.9.8.8-0ubuntu5, interfaces with PE
    disabled still get a temporary IP. Disable that check for now.
 -- Martin Pitt <email address hidden> Wed, 09 Apr 2014 15:41:11 +0200

I don't think increasing the timeout in the test in order to get it to pass is the correct approach. It's likely masking the underlying issue that we're experiencing.

------
1) The release of Ubuntu you are using, via 'lsb_release -rd' or System -> About Ubuntu
Description: Ubuntu 14.04 LTS
Release: 14.04

2) The version of the package you are using, via 'apt-cache policy pkgname' or by checking in Software Center
network-manager:
  Installed: 0.9.8.8-0ubuntu7
  Candidate: 0.9.8.8-0ubuntu7
  Version table:
 *** 0.9.8.8-0ubuntu7 0
        500 http://us.archive.ubuntu.com/ubuntu/ trusty/main amd64 Packages
        100 /var/lib/dpkg/status
isc-dhcp-client:
  Installed: 4.2.4-7ubuntu12
  Candidate: 4.2.4-7ubuntu12
  Version table:
 *** 4.2.4-7ubuntu12 0
        500 http://us.archive.ubuntu.com/ubuntu/ trusty/main amd64 Packages
        100 /var/lib/dpkg/status
isc-dhcp-common:
  Installed: 4.2.4-7ubuntu12
  Candidate: 4.2.4-7ubuntu12
  Version table:
 *** 4.2.4-7ubuntu12 0
        500 http://us.archive.ubuntu.com/ubuntu/ trusty/main amd64 Packages
        100 /var/lib/dpkg/status

3) What you expected to happen
Ethernet to "just work"

4) What happened instead
Wired ethernet times out waiting for a dhcp connection. This does not occur on the same hardware using past releases of Ubuntu. It also doesn't happen when connecting via wireless.

debug logs attached: sudo python debug-helper.py --nm debug ; tail -n0 -f /var/log/syslog | sed -e '/get_active_ap/d' -e '/dump_route/d' > /tmp/syslog