control-group: Extra border in two or more button_checked

![1](https://cloud.githubusercontent.com/assets/1333220/14210728/5a27842a-f83b-11e5-86ac-f6e962a0b560.png)
![2](https://cloud.githubusercontent.com/assets/1333220/14210737/5d5d5aac-f83b-11e5-834a-d352ed791d24.png)
