Jenkins auto-prepends PATH with path to java and ant. How to disable?

In a Free-form project I use “Inject environment variables”:

JAVA_HOME=/u01/jenkins/jdk1.8.0_181/jre
PATH=/u01/jenkins/jdk1.8.0_181/jre/bin:/u01/jenkins/apache-maven-3.0.5/bin:${PATH}

However, in shell scripts $PATH gets an additional prefix:

++ echo PATH=/u01/jenkins/jdk1.7.0_55/bin:
    /u01/jenkins/apache-ant-1.9.6/bin:/u01/jenkins/apache-maven-3.0.5/bin:
    /u01/jenkins/DependencyFinder-1.2.1-beta4/bin:
    /bin:/u01/jenkins/fly:/u01/jenkins/jdk1.7.0_55/bin:
    /u01/jenkins/jdk1.8.0_181/jre/bin:<the-original-path>

How to find what’s causing it and finally have my java 8 in path?