Quoted from this StackOverflow thread:
Using the column direction for Flexbox requires an explicit height in order for wrapping to work (see:http://codepen.io/cimmanon/pen/oyilE).(Compass multicolumn module)
If you want to have newspaper style columns without using explicit heights, the multi-column module is what you're looking for.
http://codepen.io/cimmanon/pen/CcGlE
