I've been using BS for about a month now and I absolutely love it! I think it's awesome and it's sped up my workflow quite a bit. That being said, I do a fair bit of form design, working in the financial services industry. One of the issues I'm running up against all the time is not being able to create a multi column form easily. I'm having to essentially apply columns on every single formgroup element or convert the whole form to html code and hand code the columns.
It would be nice if there was a way to define if the form could break to multiple columns as opposed to a full width single column. See example here : http://bootsnipp.com/snippets/3XrGb
Well basically that form example is incorrectly built based on how things are supposed to be constructed (http://getbootstrap.com/css/#forms).
The example has a container then a row and then the form it would probably be more correct that you put the row just inside the form so that the col(s) are the direct children of the row.
The point is, the app is working for you to help you make semantic Bootstrap sites. So if you are using the app it will put form-group inside a column and not make it the column because that is what the semantic construction is. And in doing so you will be able to use the Options pane for those columns to select the break point grid format you want. The site http://getbootstrap.com/css/#forms will tell you that form-groups can act as a row but there is not an indication that they were intended to act as columns.