copy-to-slave does nothing when the job runs on the master. This is the wrong behavior if the job is a multi-configuration project, because these jobs run with a modified workspace, depending on the parameter of the current job.

What the plugin should do when the job is running on the master, is to check if the file in the 'default' workspace is identical to the target file (it won't be in a multi-config build) and if not, copy it to the new workspace.

For example, the job on master has this workspace:
$ pwd
.../hudson/jobs/bootstrap-toolchain/workspace
$ ls
buildconf config-env.yml config.yml my-bootstrap.sh TARGET

where TARGET is the first category for the parametrization. The job will never run in this 'workspace' dir, but somewhere deep in the TARGET subdir. So copy-to-slave should copy the file from this workspace into the deep 'multi-config' workspace.

For example, when my job runs, these variables are set:
JOB_NAME=bootstrap-toolchain/TARGET=gnulinux,arch=amd64,branch=master
WORKSPACE=.../hudson/jobs/bootstrap-toolchain/workspace/TARGET/gnulinux/arch/amd64/branch/master

I hope this report is clear about the issue.