Hi Paul,
The GroupViewItem does not have a visible property to hide the items. We already have an open feature request # 407
Feature Request #407 - GroupView control does not have a Visible property to show/hide the GroupViewItems
We will try our very best to implement this feature as early as possible.
As for workaround, store the GroupBarItem to be removed, in an ArrayList and remove the GroupBarItem and restore the item back into the GroupViewCollection from the ArrayList using Insert method. Please let me know if you have any questions.
Regards,
Mano