This issue can be reproduced via carrying out the following steps:
1. Create a new Jenkins maven project
2. As a pre step, add an "execute system groovy scrip"
3. Type a simple command which throws an exception
4. Add a maven clean in the main build
5. Add a post build invoke maven target step and add a clean (tick the selection which states to only run post builds if success)
6. Save and execute the job. Observer how the groovy exception stack trace is shown at the very end and the post build step was attempted to run regardless of the groovy script failure.
(UPDATE: Changed component from groovy-plugin to m2-extra-steps-plugin. Please see comments below)