This problem appeared when I upgraded the EnvInject Plugin from 1.25 to 1.26, so the problem was probably introduced with the fix for JENKINS-12704.

I have a job with "Inject environment variables to the build process" selected, and the following line in "Properties Content":
materialize_workspace_path=${WORKSPACE}/materialize_workspace

In 1.25, this environment variable was correctly given the value
/scratch/jenkins_workspace/GDA_master.tests.RH5_64/materialize_workspace

In 1.26, this environment variable was WRONGLY given the value
/scratch/jenkins_slave//scratch/jenkins_workspace/GDA_master.tests.RH5_64/materialize_workspace