Tox keeps executing commands even when one fails

output.txt

$ tox --version
1.9.0 imported from /Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/tox/__init__.pyc

$ tox
py27 runtests: PYTHONHASHSEED='1229193552'
py27 runtests: commands[0] | echo 1
1
py27 runtests: commands[1] | false
ERROR: InvocationError: '/usr/bin/false'
py27 runtests: commands[2] | echo 2
2
py27 runtests: commands[3] | true
py27 runtests: commands[4] | echo 3
3

tox.ini

[tox]
skipsdist = True
envlist = py27

[testenv]
whitelist_externals =
    echo
    false
    true
commands =
    echo 1
    false
    echo 2
    true
    echo 3