1. Which mode of displaying validation errors you are currently using. Basically validation errors in edit mode disable most of the other operations until the error gets fixed and there is no easy way to modify this behavior.
2. We are not aware of such issue. May I ask you to send us a repro project that we would be able to debug on our side?
3. May I ask you to throw some light on this? As far as I can see RadGridView's current behavior matches your requirements. Here is a video that illustrates it.
4. I do not think that there are differences between the grouped and non-grouped scenario that should affect DataItem's PropertyChangedEvent. We could use a sample project for this too, so taht we would be able to debug it.
All the best,
the Telerik team