.panel with .sub-columns

I think this may be related to #32.

I've got a twelve column panel with some sub columns i.e: 
https://gist.github.com/rjocoleman/7762701

With the both the `.sub-columns` and `.panel` present it over-shoots the grid.
![with-panel](https://f.cloud.github.com/assets/154176/1660462/1bb43db2-5bbe-11e3-8e68-0ec838624822.png)

Without the `panel` the layout is as expected.
![without-panel](https://f.cloud.github.com/assets/154176/1660463/1c4aaa7c-5bbe-11e3-8454-78d22052745c.png)