Simultaneous test-kitchen runs as the same user on the same box results in tk runs affecting each other

gistfile1.txt

First job was started at 20:46:43, second at .. All is well until the first job runs a kitchen destroy:

These are both excerpts from job #1:

20:50:45        Finished verifying <default-centos-64-x86-64> (0m2.06s).
20:50:45 -----> Destroying <default-centos-64-x86-64>...
20:50:47        [default] Forcing shutdown of VM...
20:50:48        [default] Destroying VM and associated drives...
20:50:48        Vagrant instance <default-centos-64-x86-64> destroyed.
20:50:48        Finished destroying <default-centos-64-x86-64> (0m3.04s).
20:50:48        Finished testing <default-centos-64-x86-64> (3m54.88s).

20:52:18        Finished verifying <ubuntu-ubuntu-1204> (0m1.63s).
20:52:18 -----> Destroying <ubuntu-ubuntu-1204>...
20:52:19        [default] Forcing shutdown of VM...
20:52:21        [default] Destroying VM and associated drives...
20:52:21        Vagrant instance <ubuntu-ubuntu-1204> destroyed.
20:52:21        Finished destroying <ubuntu-ubuntu-1204> (0m3.47s).
20:52:21        Finished testing <ubuntu-ubuntu-1204> (1m32.58s).

Here's the excerpt from job #2:

20:52:26        Creating BUSSER_ROOT in /tmp/busser
20:52:26        Creating busser binstub
20:52:28 rake aborted!
20:52:28 Failed to complete #setup action: [closed stream]
20:52:28 
20:52:28 Tasks: TOP => kitchen:all => kitchen:default-centos-64-x86-64
20:52:28 (See full trace by running task with --trace)
20:52:28 Build step 'Execute shell' marked build as failure
20:52:28 Finished: FAILURE