The Postbuildscript plugin alters the order of post-build actions when executed.

Steps to reproduce :

• On a matrix configuration project
• Add a post build action of Postbuildscript
• Configure it to invoke an ant script (In my case the ant script is creating a file I want to add as an artifact)
• Add a second post build action e.g. Archive the artifacts
• Save the configuration with the post build script being first in order
• Run the job
• The archive the artifacts build step will occur first
• Re-open the job configuration and the post build action script will have moved from being the first.