Policy file not applied when updating a Cloudformation stack with changes that conflict with prior policy.

[ericraymond]

Using a policy file works at stack creation, but not upon update (migration) of a stack. The new policy is never applied.

As a workaround, we need to call set-stack-policy explicitly (via an exec task) before an update and it all works: e.g., 'aws cloudformation set-stack-policy ....'