Wordpress Version: 4.1
CMB2 Version: Master (1/16/2015)

Create a Repeatable Group, within add a repeatable select field. On page submission, after page reload you'll find additional select fields (rows) that you had not intentionally created.

https://gist.github.com/Blindmikey/bfd53603fdb2655f796c