Race condition when running two ec2test instances very close together

This seems to happen when I try o run two tests at the same time:

$ ~/src/lp-dev-utils/trunk/ec2test.py --<email address hidden> --headless
No handlers could be found for logger "boto"
Using machine image version 11
Traceback (most recent call last):
  File "/home/jml/src/lp-dev-utils/trunk/ec2test.py", line 1543, in <module>
    runner.start()
  File "/home/jml/src/lp-dev-utils/trunk/ec2test.py", line 1027, in start
    self._instance.start()
  File "/home/jml/src/lp-dev-utils/trunk/ec2test.py", line 563, in start
    self.private_key = self._controller.acquire_private_key()
  File "/home/jml/src/lp-dev-utils/trunk/ec2test.py", line 311, in acquire_private_key
    key_pair = self.conn.create_key_pair(self.name)
  File "/var/lib/python-support/python2.5/boto/ec2/connection.py", line 506, in create_key_pair
    return self.get_object('CreateKeyPair', params, KeyPair)
  File "/var/lib/python-support/python2.5/boto/connection.py", line 433, in get_object
    raise self.ResponseError(response.status, response.reason, body)
EC2ResponseError: EC2ResponseError: 400 Bad Request
<?xml version="1.0"?>
<Response><Errors><Error><Code>InvalidKeyPair.Duplicate</Code><Message>The keypair 'ec2-test-runner' already exists.</Message></Error></Errors><RequestID>0d976833-9ab5-413b-8828-793755c996ac</RequestID></Response>
no instance created