Only system environment variables are shared between jobs.
Other variables and your injected variables shouldn't be shared by other jobs.
If it is not the case, it's a bug.
Could you let me know more information?

my job injects variables from a file taken from SVN as a Build Environment step.
the job has a Execute Shell build step that calls 'env'

a first build (after Jenkins restart) behaves as expected; env prints system envirnment variables and the injected variables from the file.

I then changed the contents of the properties file, removed the properties that were there and added a new one.

subsequent builds (on the master) still print the 'old' properties.
the job triggered by this job (the node on which it is executed is actually determined by the injected variable from the properties file) also prints the old properties; it is likely that all jobs on the node (master) have access to the properties injected, therefor also likely that one job could overwrite the properties of another job if they have the same name.

(Great work by the way, much appreciated!)

Code changed in jenkins
User: Gregory
Path:
src/main/java/org/jenkinsci/plugins/envinject/service/EnvInjectActionSetter.java
http://jenkins-ci.org/commit/envinject-plugin/b3af677cb69b092b7f03b25c878f91b3c84134fe
Log:
Fixed JENKINS-10919

Fixed in 0.13

confirmed that parameters are not available to subsequent builds anymore.

thnx