I should have tracked it down earlier when I started seeing persistent UISuite failures, but I finally got around to looking at it today. We've got an annoying port conflict problem. We're setting SparkUI.DEFAULT_PORT to 3030, which is the same port that Typesafe has chosen as the default Nailgun port for Zinc server. The upshot is that if you are a developer using the Zinc server and trying to work on Spark, then you are going to see port conflicts if you don't change at least one of the default assignments.
Either we need to pick a new default spark.ui.port and change all of the docs references from 3030 to the new port, or we need to at least add a note to the developer docs to make developers aware of the conflict. https://spark-project.atlassian.net/browse/SPARK-889
