Cannot destroy spot instance request

[grahamc]

I'm getting this error when trying to destroy a spot instance request:

hydra-builder-40......> cancelling spot instance request ‘sir-ex1g53fg’... error: EC2ResponseError: 400 Bad Request
<?xml version="1.0" encoding="UTF-8"?>
<Response><Errors><Error><Code>InvalidSpotInstanceRequestID.NotFound</Code><Message>The spot instance request ID 'sir-ex1g53fg' does not exist</Message></Error></Errors><RequestID>14d327fb-390a-45c2-b35f-7e813f457d6c</RequestID></Response>

Note that before this, I got this error: https://github.com/NixOS/nixops/blob/121bdc218c050884305375758f5749b311d1f0b8/nixops/backends/ec2.py#L725