Header image mobile site

Hello,

Love the theme a lot, so first of all thank you for all the hard work. Now for my problem,

When I go to my website from a mobile device, and thus use the mobile version of your theme, the header image resizes when I click on my primary menu. What I mean is it cuts a different section of the image. My website is teamrotterdam.nl . Am I doing something wrong or is it a known issue? And is there a solution?

Again, appreciate all the hard work and keep up the good work!