Mesh tool glitch?

I found a glitch in the Illustrator Mesh Tool.

The Greyish/Purple shape leaves its space and flows through other sections polluting the gradients I'm trying to make. I've had it happen twice and the only pattern is it traces the edge of the black space. I've tried changing one of the black sections to another color and it fixes the section but the color follows the new black edge.



Anyone have any idea why it would do this.