There is an existing report for this issue, GRADLE-2263 opened on 01/May/2012. There is even a simple work around posted in the Jira.
As has been pointed out in the bug report itself, and the old forum, the ability to start and stop a jetty daemon is critical for anyone attempting to create integration tests against web applications.
The new bug system does not allow me to log in capabilities to vote for the bug, or to watch it. Suffice it to say that I spent multiple hours of tracking this down, and trying several work arounds of my own. I was disappointed to learn that this issue had been identified years ago.
The good news is that the forum software itself led me to finding the solution. As I was composing this issue the forum engine suggested other forum threads that lead me to the actual bug report.