Drush migrate-import --all=Foo broken

When trying to pass a starting migration to the --all option, nothing happens and the command returns almost immediately. Upon further investigation of migrate.drush.inc, in the drush_migrate_get_migrations() function I found:

foreach ($migration_objects as $name => $migration) {
  if (!$seen && (drupal_strtolower($start) . 'migration' == drupal_strtolower($name))) {
    //....
  }
}

None of the keys in $migration_objects has the suffix of "migration". In fact, they are all as I defined them when registering the dynamic migration classes. If I have a migration called "Foo", then the key will just be "Foo". Is this a holdover from the early days of dynamic migrations?