Symptoms
Adding extra columns to a SQL table and refreshing the service instance and then refreshing the smartobject, does not add the new columns to the smartobject.
Diagnoses
Refreshing a smartobject does not actually update it. What is does in the background, is it reloads the "current" XML definition of the SmartObject from the K2 database and check the status/consistency of its methods.
Resolution
After refreshing the service instance, you should see the new properties added to the service object. You have to "re-create" the smartobject using the refreshed service object, keeping the "original" GUID and overwrite the existing smartobject with the "new" one.