Properties in a Case (Work Item or Work Object) can only be updated through PRPC. Manually updating the column of an exposed property in the Work table has absolutely NO effect on the original value of the property embedded in the blob (pzpvStream) column. In order to update both the property embedded in the blob and the exposed column value you must formally open the case through PRPC (you can do this using the ObjOpen method in an Activity). Update the Property using the PropertySet method (also in an Activity) and then save the updated case using the ObjSave method (again from the Activity).
Thanks Henry for your response. So when the work table is altered to include a new column, and if it sits in the workpage, then the only way to update the newly created column is through an activity in PRPC. My understanding was, when we expose a property from the blob into a column in work table, the activity was required. But it seems it doesnt matter if a blob property is exposed or a new column is added to a work table, the update should happen through activity.