VS hangs using custom command with TargetType="executable" and ExecuteIn="output"

[kraigb]

PythonApplication5.zip

Repro (see attached project)

VS 15.6 Preview 2

1. Create a new Python project in VS.
2. Unload the project, edit the .pyproj file, and add the following custom command code:

$(PythonCommands);MyCommand1;MyCommand2

3. Save and reload the project.
4. Right click the project and select the command Python > Show Python files in project. Note that the .py files appear in the Output window.
5. Right click and select Python > Run ls -l.

Expected Result:
ls -l output appears in the Output window;

Actual Result:
VS hangs and eventually restarts.