Steps to reproduce it:
1. Create a WF job with some dummy script
2. Run a build (or two)
3. Rename the job
4. Restart Jenkins
5. You have unreadable data warnings in "Manage Jenkins"
The root cause is in build.xml files, where the job name is not properly changed in the rename process:
Behavior checked using Jenkins 1.580.2 + Workflow 1.4 and 1.609.1 + Workflow 1.8