Isn’t IE awesome?…
When vertically aligning elements in the page header, we use flexbox (least hacky way to do it).
Unfortunately, IE11 has a bug with flexbox and respecting max-width elements: https://connect.microsoft.com/IE/feedbackdetail/view/951267/horizontal-scrolling-with-flex-grow-max-width
Looks like they decided to fix it in Edge, but they’re not interesting in fixing anything but security (I guess that’s good) issues in IE anymore.
If you need IE support, you might need to remove the vertical centering.