ToolbarItems not showing on a TabbedPage

Hello,
i try to add ToolbarItems on my TabbedPage, but they are not shown when the TabbedPage appears the first time.
Then, if i swipe or click on a tab, the app title disappears and the toolbarItems appear.
What am i missing ?

Here is the xaml of my TabbedPage :

<?xml version="1.0" encoding="utf-8" ?>
<TabbedPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:view="clr-namespace:AppTitle.Forms.Views"
             x:Class="AppTitle.Forms.Views.MainPage"
             Title="APP TITLE"    
            >
  <TabbedPage.ToolbarItems>
    <ToolbarItem  x:Name="itemMenu_help" Command="{Binding NavigateToDocumentation}" Icon="action_help.png" Text="Docs"  />
    <ToolbarItem  x:Name="itemMenu_share" Command="{Binding ShareReportCommand}" Icon="action_share.png" Text="Share"  />
  </TabbedPage.ToolbarItems>

  <TabbedPage.Children>
    <view:SaisiePage Title="PARAMETRES DE CALCUL"    />
    <view:ResultatsPage Title="RESULTATS"  />
    <view:GraphiquePage Title="GRAPHIQUE"  />
  </TabbedPage.Children>

</TabbedPage>

How to have the ToolbarItems, on the right, right from the loading of the TabbedPage and, Icon and app title left aligned ?

One more time, thanks in advance, for your help.
Thomas