Using task listeners in multi-project parallel build

I am running tasks in parallel in a multi-project build. javaDoc and createDB are two tasks running in parallel. I have a listener added in javaDoc task and I log the output of javaDoc task to a file using the listener.onOutput(CharSequence output). Running build in sequence seems fine.

But when running in parallel the standard output of createDB are also captured by the listener registered for javaDoc task.