If the project build is cancelled via WEB UI then ANT process is still shown in
OS process list.
Possible solution: change hudson/tasks/Ant.java, method perform(...):
......
Proc antProc = null;
try {
antProc = launcher.launch(args.toCommandArray(),env,
listener.getLogger(),proj.getModuleRoot());
int r = antProc.join();
return r==0;
} catch (InterruptedException ie){
antProc.kill();
} catch (IOException e) {
......

Thanks!