The "Inject Environment Variables" build step does not allow for multiple build steps, but simply duplicates the first "Inject Environment Variables" build step regardless of the content that was added.

Steps to reproduce:
1) In the build steps phase, add "Inject Environment Variables" build step
2) Fill the build step in with something (Properties File Path or Properties Content does not matter).
3) Add another "Inject Environment Variables" build step.
4) Fill in that build step as well with something different
5) Select Save
6) Select configure again to return to the job configuration

Result:
Both "Inject Environment Variables" content will display identical data, which will be the value of that from step #2 above. So essentially there is no way to invoke environment variables in multiple build steps.