Tabbed page + navigation + listview. Bug?

Hi guys.

I'm developing a app with Xamarin.Forms with this setup:

Tabbed page as detail of Master detail, using navigation page for browsing.

Two listviews, one for each tab.

I have an event on listview.ItemTapped that calls another page with await Navigation.PushAsync(new Detail(oferta));

Now the bug:
After dispposing the "Detail" page, I can't switch tabs. It looks weird, look:

I tried changing to .PushModalAsync, that stopped the problem. But I want the navigation bar with the back button.

Am I missing something?

Thanks.