Incorrect column size

Hey,

I noticed a possible issue with the small column widths. I've got 2 columns each at 50% for all 3 screen sizes (`.grid-row-col-6-12--{sm/md/lg}`). There's a title on the left and a button on the right. When collapsed to < 32rem (512px I think), they both stay at 100% width. Where as they should stay at 50% each.

Here's a [gist](https://gist.github.com/eliquious/a1401f4fa9d4702135a6).

The md and lg sizes work fine. It seems to be the `flex-basis: 100%` rule causing the issue. Any ideas?