When Top bar is enabled, the nav bar has jerk when scrolling

[loudweb]

Hi
when the top bar is enabled, the navigation header bar gives a jerk when scrolling up and down.

Can this be resolved.

http://www.lawimage.com.au is the production site.
I’ve also installed a test site with clean WP and straight Unicon Theme without any CSS changes. You can see the navbar jerk there too.

Can a resolution be provided.

thanks

Ticket