virtualenv: Scripts installed with wrong shebang under subprocess

On Python 3.5.1 but not on 2.7.10, when I invoke pip through a subprocess in a virtualenv, the scripts are created with the wrong shebang and thus fail to run:

$ cat > invoke.py
import sys
import subprocess

subprocess.Popen(sys.argv[1:]).wait()
$ rm -Rf env
$ python -m virtualenv --version
14.0.0
$ python --version
Python 3.5.1
$ python -m virtualenv env
Using base prefix '/Library/Frameworks/Python.framework/Versions/3.5'
New python executable in /Users/jaraco/Dropbox/code/public/aspen/env/bin/python3
Also creating executable in /Users/jaraco/Dropbox/code/public/aspen/env/bin/python
Installing setuptools, pip, wheel...done.
$ python invoke.py env/bin/pip install pytest
Collecting pytest
  Using cached pytest-2.8.5-py2.py3-none-any.whl
Collecting py>=1.4.29 (from pytest)
  Using cached py-1.4.31-py2.py3-none-any.whl
Installing collected packages: py, pytest
Successfully installed py-1.4.31 pytest-2.8.5
$ head -n 1 env/bin/py.test
#!/Library/Frameworks/Python.framework/Versions/3.5/bin/python3

One would expect the py.test script to have a shebang with ‘env’ in it.

Using pyvenv instead is not subject to the issue. Removing the __PYVENV_LAUNCHER__ environment variable before launching the subprocess works around the issue, as reported here. The issue was observed with 13.1.2 and 14.0.0.

Is this behavior expected? If so, is removing the environment variable the appropriate thing for a parent process to do to work around the issue?