--group option missing?

I'm still somewhat new to Drupal, so if I'm making a total newbie mistake, please don't hesitate to tell me.

I love Migrate, as it perfectly fits the project I'm working on, but I'm totally flummoxed by this supposed drush migrate-import --group=name command.

The migrate_example module has examples and instructions for its use, the documentation here on drupal.org has the same, even the group.inc file exists and has plenry of group-related code... but when I try to actually use drush migrate-import --group=name, I get the following error:

Unknown option: --group.  See `drush help migrate-import` for available options. To suppress this error, add the option --strict=0.                                                                                              [error]

I've got a migration class called MRUserMigration written, and it works when I execute drush mi MRUser, so the rest of the system seems fine.

Am I doing something wrong? I'm using Migrate 7.x-2.2 on Drupal 7.12, running in OSX 10.6 on Apache, with Drush 5.0-dev. I've used drush cc all, since I read that it might help, but it didn't work.