Weird navigation bar

Hi,

we’re experiencing a weird issue with the navigation bar on the shop-page.

Screenshot:

View post on imgur.com

Interestingly, all Header-Styles with custom text in it work just properly without any problem, however, the Logo + Navigation headers (both of them) will produce a navigation bar that looks pretty weird.

We’ve not touched any CSS whatsoever – reinstalling the theme results in same output.

Any ideas?