Drush hangs when trying to bootstrap Drupal Running Ubuntu 12.04 with the 14.04 backports for Drush (meaning we are running Drush 5.10.0)

After importing the database (with drush sqlc &lt; dump.sql), Drupal is no longer able to be bootstrapped by Drush.

drupal-site@uat-previewweb1:/var/www/drupal/uat-preview/current$ drush st -v -d
Bootstrap to phase 0. [0.01 sec, 3.81 MB]                            [bootstrap]
Drush bootstrap phase : _drush_bootstrap_drush() [0.01 sec, 4.04 MB] [bootstrap]
Loading drushrc "/etc/drush/drushrc.php" into "system" scope. [0.01 sec, 4.04 MB]                                                                            [bootstrap]
Cache HIT cid: 5.10.0-commandfiles-0-42f7d1cb79623ad6de6c23932c9a4e2b [0.02 sec, 4.07 MB]                                                                        [debug]
Bootstrap to phase 0. [0.06 sec, 9.04 MB]                                                                                                                    [bootstrap]
Drush bootstrap phase : _drush_bootstrap_drupal_root() [0.08 sec, 9.04 MB]                                                                                   [bootstrap]
Initialized Drupal 7.31 root directory at /var/www/drupal/uat-preview/releases/20140911-4 [0.09 sec, 10.69 MB]                                          [notice]
Drush bootstrap phase : _drush_bootstrap_drupal_site() [0.09 sec, 10.7 MB]                                                                                   [bootstrap]
Initialized Drupal site uat-preview at sites/default [0.09 sec, 10.7 MB]                                                                                [notice]
Cache HIT cid: 5.10.0-commandfiles-2-c32acd775c18a90c5b41d0fc9accf5ab [0.09 sec, 10.71 MB]                                                                       [debug]
Drush bootstrap phase : _drush_bootstrap_drupal_configuration() [0.1 sec, 10.75 MB]                                                                          [bootstrap]
Drush bootstrap phase : _drush_bootstrap_drupal_database() [0.1 sec, 10.81 MB]                                                                               [bootstrap]
Successfully connected to the Drupal database. [0.1 sec, 10.81 MB]                                                                                           [bootstrap]
Drush bootstrap phase : _drush_bootstrap_drupal_full() [0.12 sec, 11.92 MB]                                                                                  [bootstrap]


The command hangs here and does not return.

Does anyone have any ideas on what could be causing this? Is it worth it to stray from debian packages and run Drush 6.4.0 here?
In this particular case, the issue was with an incorrectly configured memcache server settings, the Drupal environment in question was attempting to communicate with a memcache instance that had a firewall dropping all connections.

The fix was to configure memcache servers in the Drupal settings file. Hope this helps someone else.