I have configured an External Shell M2 Extra Steps post build step. I configured
it to only be executed if the build was a success. The build is a maven goal of
release:prepare. The build succeeds but the post step does not execute.

I added a pre build step, this was executed. I removed the pre build step.

I modified the config to run the post build step if the build was either
successful or unstable. The job ran, the build was a success but the post build
step did not run.

I modified the config to run the post build step "Run regardless of build
result". I ran the job, the build was a success and the post build step was run.

It appears that the post build shell script step is only run if the Post Build
Run Criteria is set to "Run regardless of build result"