If you update the value from the UI, then the item should be regrouped. Otherwise, if you update the value of the property (Changed) from code, then you should ensure a CollectionChanged notification is raised so that the UI is notified for the change. When you manually sort, group or invoke a Rebind(), a CollectionChanged notification with Action Reset is raised. This is the reason why the value is updated. You can check this article
for more details. It is for updating the aggregates, however, the idea regarding updating the item with the changed property would be the same.
You say that the solution you found creates another bug, resetting the GridViewScrollBar. The reason for this that every data operation, plus invoking a Rebind() will raise a CollectionChanged event with Action System.Collections.Specialized.NotifyCollectionChangedAction.Reset. Please note that just sorting any column from your RadGridView will invoke a Rebind internally.
I can recommend you using the approach from the Update item outside RadGridView help article. That way such a notification will be raised just for the item being actually changed. As a result, the item will be updated without resetting the GridViewScrollBar.
I hope this helps.
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