IE11 Flexbox resizing issue

I've made a nested flexbox site. The main row consists of two colums. The second column consists of two rows and two columns. It works fine (flexible) in Opera, Firefox, Chrome, Android and Safari-mobile. Only in IE, I can't get de boxes flexible. Content overflows de boxes when resizing in IE11.

See example:  https://jsfiddle.net/vf9wLjp5/1