I have a legacy v7 site for which we need to cancel any move operations for certain doctypes unless the user is in certain groups.

Using a ContentService.Moving event handler we can cancel the move easy enough however the event message does not bubble up the UI and the move action gets confirmed with a success message even though the node was not moved. Here is the event handler...

private void ContentServiceOnMoving(IContentService sender, MoveEventArgs<IContent> e)
{
    var restrictedDoctypes = new[]
    {
        Blog.ModelTypeAlias, 
        NewsSection.ModelTypeAlias, 
        PressRelease.ModelTypeAlias
    };

    var doctypesBeingMoved = e.MoveInfoCollection.Select(d => d.Entity.ContentType.Alias);

    if (!restrictedDoctypes.ContainsAny(doctypesBeingMoved) || !e.CanCancel) return;

    e.CancelOperation(new EventMessage("Content Permissions", "You do not have permission to move this type of document", EventMessageType.Error));
}

I have also tried the following with no success:

e.Cancel = true;
e.Messages.Add(new EventMessage("Content Permissions", "You do not have permission to move this type of document", EventMessageType.Error));

Any ideas on how to force this message up to the UI?