There are numerous Flexbox bugs in IE11 and other browsers - see flexbox on Can I Use -> Known Issues, where the following are listed under IE11:
display: flex
and flex-direction: column
will not properly calculate their flexed childrens' sizes if the container has min-height
but no explicit height
propertymin-height
is usedAlso see Philip Walton's Flexbugs list of issues and workarounds.