Fix the vertical divider origin to match the bottom of the horizontal divider

Before:

![before](https://cloud.githubusercontent.com/assets/14093/2859484/5cb47958-d1a7-11e3-92a6-51a4cbf2a0bb.png)

After:

![after](https://cloud.githubusercontent.com/assets/14093/2859485/60497370-d1a7-11e3-9897-e68ffe9e4fb5.png)