I might have found a small bug?
When you have the search-field enabled and you narrow the browser window to minimal. When it’s small enough, menu changes to menu opening button. When you click the button and it opens the menu, search-field is left on top of the menu. I guess it should be below the opened menu?
Otherwise really smooth responsive design!
One thing which I forgot to mention is, that this happens only if the site name consists of multiple and longish words.
When browser window is squeezed, words are divided to separate lines and this breaks the original layout causing the problem.
So, after all not so critical bug..