It looked fine when I composed it.
I interpret this artefact as subtle hint from Tableau that bad things sometimes happen to people who rock the boat. Like accidentally stepping into a tub of concrete that then quickly sets and accidentally slides into a nearby body of water.
I'm interpreting this comment of yours as you being a kindred spirit who fights against paranoid delusions everyday! Just kidding. Really!
What, you don't believe me?! Well f---- you ....
Just kidding, really.
Unfortunately this is not resolved in Tableau Public exports as of this post (v.11/20/13) - legends removed in Tableau Public (i.e., the Desktop parallel) are not suppressed in PDF exports.