Admin bar disturbs header when logged in

First off: I love your theme. Really good work.

But I′ve found one annoying thing: When logged in as admin worpress provides the black admin bar on top of the page as an overlay.

When beeing logged in and starting to scroll down a page, the header gets rezised / smaller / partially hides behind the admin bar.

This is how the header looks like when opening the page:

This is how the header looks like scrolling down:

This is annoying when working on the page beeing logged in.

Can you please fix that?