The Verify_Data_Loss_msg is indeed not shown when a view is hidden in the desktop style. We likely did not do this because your changes would still be there when you switch back to the view you leave. Part of this is probably that we experimented with an MDI layout in the initial development stages of the Web Framework. Unfortunately OnHide is not cancellable right now so there is no proper way to do this unless you augment Show on all the views that the user can open.