Steps to create:

1. Start a Hudson instance with minimal set of plugins
2. Checkout cobertura source tree from SVN
3. Point the workspace to this tree as per the attached config.xml
4. This error occurs on each build

This is reproducible in this workspace.

coverage:

BUILD SUCCESSFUL
Total time: 10 minutes 57 seconds
FATAL: Releasing unallocated workspace c:\Hudson\cobertura
java.lang.AssertionError: Releasing unallocated workspace c:\Hudson\cobertura
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)