It appears that console hosted Windows Workflow applications hang and CPU usage climbs to 100% when executing the CreateWorkflow method from program.cs when
Mailframe's Testrunner is installed on the same machine. Testrunner is a Visual Studio add-in that integrates running NUnit tests and provides test performance and coverage metrics (good when a project's unit tests were previously written with NUnit, or you don't have or wish to purchase a VSTS license). Removing Testrunner seems to fully resolve this problem.