Listview Item Selected Highlight

Ciao
I have two questions about selected item in a listview:
1- in a "grouped listview", if I tap a row, I don't have the row highlighted. I don't know why.
2- in a "non grouped listview", if I tap a row, I have the row highlighted. I would like not to have the row highlithed, so I use this code

listView.ItemSelected += (sender, e) => {
 if (e.SelectedItem == null) return; // don't do anything if we just de-selected the row
 // do something with e.SelectedItem
 ((ListView)sender).SelectedItem = null; // de-select the row
 };

It works, but I have a very fast "flash" (passing from highlighed to no-highlighted status). Is it possible not to have this "flash"?