File Scripts do not expose Build variables

I have a script in /var/tmp that simply executes "env" – the output of which follows:

16-Jan-2014 18:29:35 Starting task 'Print Env' of type 'com.atlassian.bamboo.plugins.scripttask:task.builder.script'
16-Jan-2014 18:29:35
Beginning to execute external process for build 'XXXX #5 (XXXX-5)'
... running command line:
/bin/sh /var/tmp/env.sh
... in: /opt/atlassian/bamboo/current/xml-data/build-dir/XXXX
16-Jan-2014 18:29:35 TERM=xterm
16-Jan-2014 18:29:35 JAVA_OPTS=-XX:MaxPermSize=256m -Xms256m -Xmx384m
16-Jan-2014 18:29:35 LD_LIBRARY_PATH=/usr/java/jdk1.6.0_27/jre/lib/amd64/server:/usr/java/jdk1.6.0_27/jre/lib/amd64:/usr/java/jdk1.6.0_27/jre/../lib/amd64
16-Jan-2014 18:29:35 NLSPATH=/usr/dt/lib/nls/msg/%L/%N.cat
16-Jan-2014 18:29:35 PATH=/sbin:/usr/sbin:/bin:/usr/bin
16-Jan-2014 18:29:35 _=/bin/env
16-Jan-2014 18:29:35 PWD=/opt/atlassian/bamboo/atlassian-bamboo-5.3/xml-data/build-dir/XXXX
16-Jan-2014 18:29:35 JAVA_HOME=/usr/java/latest
16-Jan-2014 18:29:35 JAVA_PERMGEN_SUPPORTED=true
16-Jan-2014 18:29:35 XFILESEARCHPATH=/usr/dt/app-defaults/%L/Dt
16-Jan-2014 18:29:35 SHLVL=4
16-Jan-2014 18:29:35 Finished task 'Print Env'

As you can plainly see, the variables are nowhere in there.

I see people complaining about these variables not being populated all the way back to the 4.x series. What's going on?