@grid-columns ignored

I have customised Bootstrap at http://getbootstrap.com/customize/ and set the @grid-columns to 18. Then in Bootstrap Studio, I create a new design, go to File > Design Settings > Manage Themes button > Import the generated bootstrap.min.css and select that for the design (as detailed here)

Now if I add a new row and then a column, the column is set to class="col-md-12", if I select the column and look at the Column Size (or offset/push/pull) selects for LG/MD/SM/XS under Options on the right, they still only go up to 12, not 18. It does however show extra space in the row to the right of the column, so it seems to sorta-kinda notice the correct number.

Am I missing something obvious here?

I don't know, but I have a feeling that the app doesn't literally read the bootstrap css file to get it's options from. The Dev's I'm sure set their own option config as the default based on the default bootstrap css structure. I'm wondering if the SASS support that is coming will make a difference with this in your particular situation.