In a MultiJob Project in the MultiJob Phase the Predefined parameters are no longer being passed to the phase project. In Jenkins version 1.651.1 or prior I defined env vars $PARENT_WORKSPACE and $UNIFIED_BUILD_NUMBER, using Inject Environment Variable.
Then I passed these as Predefined Parameters to the Phase project. In the Phase project, the environment variables were undefined.
After I upgraded to 1.651.2 this stopped working. Then I downgraded back to 1.651.1 and the functionality was restored.