$GOPATH/bin/juju and tools mismatch failures

I’ve recently seen Juju failures where Juju commands fail rather than queue up like they are supposed to.  Here is the output of running my shell script to deploy the GUI:

/home/bac/projects/juju-gui> deploy-gui.sh
+ /home/bac/work/bin/juju bootstrap --upload-tools
+ /home/bac/work/bin/juju deploy 'cs:~juju-gui/precise/juju-gui'
error: no instances found
+ /home/bac/work/bin/juju set juju-gui juju-gui-source=lp:juju-gui
error: no instances found
+ /home/bac/work/bin/juju expose juju-gui
error: no instances found

The problem appears to be a mismatch between my version of juju and the tools. Updating the juju source and rebuilding solves the problem.