I have Ubuntu 12.04 and Tarantool 1.6.8, pulled from source today from tarantool-1.6.
I execute these requests:

box.cfg{}
box.schema.user.info('guest')
box.schema.user.drop('guest')
box.schema.user.info('guest')

The box.schema.user.drop('guest') request fails with the message:

- error: 'Failed to drop user ''guest'': the user is a system user

and that's fine. However, the second box.schema.user.info('guest')
request now returns nothing. I see:

tarantool> box.schema.user.info('guest')

---
- []
...