hierarchical workflow failing only when integrity checking is on

The workflow in question is depicted here:

https://github.com/pegasus-isi/pegasus-workflow-development-environment/blob/master/shared-data/sample-hierarchical-wf/diagram.svg

The workflow script is attached, and running it with integrity checking on should cause the workflow to fail.

Is this an issue with the workflow generation script or do we have an underlying bug?