I use "free-style software project"
If I specify:
Advanced Project Options/custom workspace = C:/tmp/test (any folder)

I always have error - FATAL: Releasing unallocated workspace C:/tmp/test
It brakes my build system

FATAL: Releasing unallocated workspace C:/tmp/test
java.lang.AssertionError: Releasing unallocated workspace C:/tmp/test
at hudson.slaves.WorkspaceList.release(WorkspaceList.java:74)
at hudson.model.AbstractBuild$AbstractRunner.run(AbstractBuild.java:365)
at hudson.model.Run.run(Run.java:1090)
at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:46)
at hudson.model.ResourceController.execute(ResourceController.java:93)
at hudson.model.Executor.run(Executor.java:122)