When you exercise a deploy target in the maven build.xml file (created when building a release), you either write to a local maven repo or a distant one. You can deploy twice the same jar to a local repo, but when you do it to a distant repo, it doesn't generally let you delete the to-be-overwritten artifact. This results in your ant deployment script's public suicide.
This particular case happens with the javadoc.jar generated for the scala-library (see attached log).
Examining the src/build/maven/maven-deploy.xml maven deployment file with git blame shows the javadoc jars were added to deployment targets by Josh in 2012, but a previous extra-attachement stanza existed from an addition by Lukas in 2008.