Empty last column (subnav links do not list evenly)

[ln2341]

We don't know why our fourth column won't always populate with links?
As shown in the screenshots below, the problem is that the subnav for the About Us section seems to be stacked to the left, whereas the other sections are spread out evenly - we would like to list them evenly like in screenshot #1.

I've tried recreating the issue here: https://jsfiddle.net/ln2341/y7ujwgu8/17/

Screenshot #1: Links are columnized correctly in four columns

Screenshot #2: We would like to list four links at the top and two links at the bottom, i.e. always fill out the fourth column