We have the following project at Maven:
https://builds.apache.org/job/core-integration-testing-maven-3-trunk-windows/

It is a freeform project, with a Maven build step. It was previously configured with the following under Advanced > Properties:

maven.home="$WORKSPACE/apache-maven-3.0-SNAPSHOT"

However, the resulting command line was:

... -Dmaven.home="f:hudsonhudson-slaveworkspacecore-integration-testing-maven-3-trunk-windows/apache-maven-3.0-SNAPSHOT" ...

(see https://builds.apache.org/job/core-integration-testing-maven-3-trunk-windows/14/consoleText)

Moving this to the "goals" line instead resolved the issue.