Comment 40 for bug 33968

This fix should help a bit, too:

 dhcp3 (3.0.3-6ubuntu7) dapper; urgency=low
 .
   * debian/patches/deroot-client.dpatch: Fixed major thinko in lease file
     handling: dhclient was unable to update the leases file after it
     daemonized, which meant that 'sudo dhclient ethX' worked fine, but
     obtained leases at boot time were never written if the first attempt timed
     out. Now make sure that the lease file is always writable by forked
     instances, too. Closes: LP#39249 (and should also mitigate #33968).
   * Add debian/patches/dhcpd.conf-subnet-examples.dpatch: Add 'option
     subnet-mask' to example dhcpd.conf. Closes: LP#26661

However, the actual solution is highly nontrivial and non-straightforward, please see upstream's reply at
http://marc.theaimsgroup.com/?l=dhcp-users&m=114624286102709&w=2.