The first two of the four boxes are given box-flex:1, and the last two are given widths (which are correct). Box-flex is working to fill the remaining space but not equally (*width of box-flex divs seems to be based on the amount of content, not an even splitting of the rest of the space).
1 - Lorem Ipsum only a little bit now. Lorem Ipsum only a little bit now. But add even a slight difference...
2 - Lorem Ipsum only a little bit now. Lorem Ipsum only a little bit now.
3 - Lorem Ipsum only a little bit now. Lorem Ipsum only a little bit now. Vary the content be even a tiny bit, and the box with more content (or the first one) will grow larger than the rest.
4 - Lorem Ipsum only a little bit now. Lorem Ipsum only a little bit now.