No, the black part doesn't move. This is confusing. I'm thinking that it's like nruddock said - there's some stray geometry in there somewhere. It looks like it because of the way the black area is n a triangular shape across part of the flat surfaces. Not sure how to handle it though.

Here's the link to my freebies:   https://www.renderosity.com/mod/freestuff/?uid=493127

My cousin Jack can speak to beans. That's right.... Jack and the beans talk