Import wizard and missing events

We have on a part subclass one attribute that is depending on three other attributes - the value of this attribute is calculated based on the values of the other values. This is done by a px-extension called via an update-title-block-event on the subclass and works if we do it in the GUI.But sometimes a greater amount of parts should be updated and this could be easer done in Excel.
So we searched the objects, exported to Excel, changed there and used the import wizard to update the parts. Well, the three parts were updated but the dependend one not.