Composer download hook running past 160M with Gelf module install

Running drush dl gelf with composer module installed throws the error below. Shouldn't 160M php memory be enough?

Install location /vagrant/data/html/example/sites/all/modules/gelf already exists. Do you want to overwrite it? (y/n): y
Calling _drush_recursive_copy(/tmp/drush_tmp_1341592633_4ff71439a9e01/gelf, /vagrant/data/html/example/sites/all/modules/gelf) [6.11 sec, 37.12 MB]                         [debug]
Project gelf (7.x-1.x-dev) downloaded to /vagrant/data/html/example/sites/all/modules/gelf. [6.15 sec, 37.12 MB]                                                        [success]
PHP Fatal error:  Allowed memory size of 167772160 bytes exhausted (tried to allocate 305529 bytes) in /home/vagrant/.drush/composer/vendor/composer/composer/src/Composer/Json/JsonFile.php on line 275
PHP Stack trace:
PHP   1. {main}() /usr/share/php/drush/drush.php:0
PHP   2. drush_main() /usr/share/php/drush/drush.php:14
PHP   3. _drush_bootstrap_and_dispatch() /usr/share/php/drush/drush.php:59
PHP   4. drush_dispatch() /usr/share/php/drush/drush.php:90
PHP   5. call_user_func_array() /usr/share/php/drush/includes/command.inc:165
PHP   6. drush_command() /usr/share/php/drush/includes/command.inc:165
PHP   7. _drush_invoke_hooks() /usr/share/php/drush/includes/command.inc:198
PHP   8. call_user_func_array() /usr/share/php/drush/includes/command.inc:324
PHP   9. drush_pm_download() /usr/share/php/drush/includes/command.inc:324
PHP  10. drush_command_invoke_all() /usr/share/php/drush/commands/pm/download.pm.inc:205
PHP  11. call_user_func_array() /usr/share/php/drush/includes/command.inc:1179
PHP  12. drush_command_invoke_all_ref() /usr/share/php/drush/includes/command.inc:1179
PHP  13. call_user_func_array() /usr/share/php/drush/includes/command.inc:1195
PHP  14. composer_drush_pm_post_download() /usr/share/php/drush/includes/command.inc:1195
PHP  15. drush_composer() /home/vagrant/.drush/composer/composer.drush.inc:109
PHP  16. Composer\Console\Application->run() /home/vagrant/.drush/composer/composer.drush.inc:91
PHP  17. Symfony\Component\Console\Application->run() /home/vagrant/.drush/composer/vendor/composer/composer/src/Composer/Console/Application.php:66
PHP  18. Composer\Console\Application->doRun() /home/vagrant/.drush/composer/vendor/symfony/console/Symfony/Component/Console/Application.php:106
PHP  19. Symfony\Component\Console\Application->doRun() /home/vagrant/.drush/composer/vendor/composer/composer/src/Composer/Console/Application.php:86
PHP  20. Symfony\Component\Console\Command\Command->run() /home/vagrant/.drush/composer/vendor/symfony/console/Symfony/Component/Console/Application.php:193
PHP  21. Composer\Command\InstallCommand->execute() /home/vagrant/.drush/composer/vendor/symfony/console/Symfony/Component/Console/Command/Command.php:239
PHP  22. Composer\Installer->run() /home/vagrant/.drush/composer/vendor/composer/composer/src/Composer/Command/InstallCommand.php:64
PHP  23. Composer\Installer->doInstall() /home/vagrant/.drush/composer/vendor/composer/composer/src/Composer/Installer.php:178
PHP  24. Composer\DependencyResolver\Pool->addRepository() /home/vagrant/.drush/composer/vendor/composer/composer/src/Composer/Installer.php:247
PHP  25. Composer\Repository\ArrayRepository->getPackages() /home/vagrant/.drush/composer/vendor/composer/composer/src/Composer/DependencyResolver/Pool.php:66
PHP  26. Composer\Repository\ComposerRepository->initialize() /home/vagrant/.drush/composer/vendor/composer/composer/src/Composer/Repository/ArrayRepository.php:144
PHP  27. Composer\Repository\ComposerRepository->loadRepository() /home/vagrant/.drush/composer/vendor/composer/composer/src/Composer/Repository/ComposerRepository.php:104
PHP  28. Composer\Json\JsonFile->read() /home/vagrant/.drush/composer/vendor/composer/composer/src/Composer/Repository/ComposerRepository.php:134
PHP  29. Composer\Json\JsonFile::parseJson() /home/vagrant/.drush/composer/vendor/composer/composer/src/Composer/Json/JsonFile.php:90
PHP  30. json_decode() /home/vagrant/.drush/composer/vendor/composer/composer/src/Composer/Json/JsonFile.php:275
Drush command terminated abnormally due to an unrecoverable error.                                                                                                      [error]
Error: Allowed memory size of 167772160 bytes exhausted (tried to allocate 305529 bytes) in
/home/vagrant/.drush/composer/vendor/composer/composer/src/Composer/Json/JsonFile.php, line 275 [20.64 sec, 159.74 MB]
vagrant@lucid64:/vagrant/data/html/example$ 

Steps to reproduce (on a Mac):

curl -L get.rvm.io | bash -s 1.14.1
exec $SHELL
rvm reload
git clone --branch release/1.0.0 https://github.com/myplanetdigital/ariadne.git /tmp/ariadne-composer-bug
cd /tmp/ariadne-composer-bug
rake setup
vagrant up
vagrant ssh
cd /vagrant/data/html/example
drush dl composer
drush dl gelf

Cleanup

cd /tmp/ariadne-composer-bug
vagrant destroy --force