When using a variable in a custom workspace, it doesn't get replaced for copy-to-slave.

I see correctly "Building remotely on Jenkins-Worker-01 (Remote-Worker) in workspace /var/lib/jenkins/jobs/a_name/workspace" in the log and "/var/lib/jenkins/jobs/a_name/workspace" is the $PARAMETER. But the copytoslave uses $PARAMETER as a string...
Interesting point is, it gets resolved correctly for the slave, but not the master.

How to reproduce:

• Creating a project with "Use custom workspace: $PARAMETER"
• Enable "Copy files into the job's workspace before building" with "This job's workspace on the master (not advised)"
• Start the build with $PARAMETER=/var/lib/jenkins/jobs/a_job/workspace/

Got:
[copy-to-slave] Copying '.,*', excluding '/.git/,*/.gitignore', from 'file:/$%7BPARAMETER%7D' on the master to 'file:/var/lib/jenkins/jobs/a_job/workspace/' on 'slave'.

Expected:
[copy-to-slave] Copying '.,*', excluding '/.git/,*/.gitignore', from 'file:/var/lib/jenkins/jobs/a_job/workspace/' on the master to 'file:/var/lib/jenkins/jobs/a_job/workspace/' on 'slave'.