[bug][safari] Clearing the search text input janks the page until blurred

I noticed a bug when using the search box, when I backspace all my text and make it empty, the header becomes a bit taller and janks the page.

Normal, starts at 40px:

After typing some text and backspacing it jumps to 46px.

I was curious what was happening so I tried it in Chrome and couldn't reproduce it. But then through a process of elimination found that the flex class on the <input> is the culprit. Deleting flex fixes the issue. I don't think it should be necessary anyway because I think flex is only necessary for elements with children.

I don't know why Safari behaves like this though.