If the EnvInject v0.9 is INSTALLED into Jenkins, Jenkins build jobs will no longer have their per-job variables available. Some of these variables are things like WORKSPACE, BUILD_NUMBER, etc.
To test, install EnvInject v0.9. Create a simple job with a single Execute Windows batch command whose only command is "set". Run the job with EnvInject - you'll see some variables. Uninstall or disable EnvInject, restart Jenkins, run the same job - more variables will be seen.
Reason I marked this a "Blocker" - a workspace clean out command wiped our hard drive. Several of our jobs have a command like this "del %WORKSPACE%*.* /s /q". This has always worked nicely in the past, clear back to Hudson days. But run it with EnvInject v0.9 and it will wipe the drive - which the job proceeded to do.