MDL checkboxes don't work with column-count

` to make two nice columns. They all look fine, but the checkboxes in the second column don't work quite right.

Here's an example: http://codepen.io/anon/pen/eJMxpQ

In Safari 9, I get 3 checkboxes in the first column, and 1 checkbox in the second column. The first 3 checkboxes work great. The one in the second column is funny. The border of the box does change from gray to blue and back, but it never fills. When you click the box, the "touch" circle appears in both the bottom of the first column, and in the second column.

In Firefox, when using the `-moz-` prefix, they work great.

In Chrome, when using the `-webkit-` prefix, they are broken in the same way as Safari, except that the "touch" circle never appears at all.

I haven't tried Explorer yet.

I'm using MDL 1.0.6, and the latest version (AFAIK) of each of these browsers.