I see that HidePrefix hides fields from being shown in the selection state box. However, fields are still visible for creation of new listboxes, tabular diagrams etc. So this seems to be the same and normal behaviour in QView as in QSense.
All field names beginning with this text string will be hidden in the same manner as the system fields. A user-defined variable. Example: set HidePrefix='_' ; Ifthis statement is used, the field names beginning with an underscore will not be shown in the field name lists when the system fields are hidden.