I am using MP6, and I like it a lot.
There is a bug in MP6 on OS X Safari. I am using Safari version 6.0.5 (8536.30.1) on OS X 10.8.4, but the bug may exist on other versions of Safari, OS X, or other web browsers.
When you load any wp-admin page, the WordPress "W" menu in the upper left is "stuck" open. As soon as the page loads and you move your mouse, anywhere, the menu closes.
Specifically, the menu that is stuck open is:
li.wp-admin-bar-wp-logo div.wp-admin-bar-wp-logo. It says things like, "About WordPress, WordPress.org, Documentation, Support Forums, Feedback."
To fix this bug, the "W" menu shouldn't be open when I load an admin page using Safari.
If you have questions, please let me know and I am happy to provide additional details.