Hi Tom,
A muti-select list box is tied to one field in your form. Once promoted as a property to you library, all of the values are concatenated because there is only on row of data. You would need to have each selection as a separate field in your form, or use default data with a repeating data structure that could then be pushed out to a list through CAML or qRules SubmitToSharePointList.
Hope that helps!
Bre