Two titleviews in dotnet maui - xaml

Question

Im trying to create a Maui application with a dynamic Tabbar which should also be navigateable (and thus consist of NavigationPages). When I switch to a different tab, everything works fine, but as soon as is switch to an alreay visited tab, two titlebars appear:
One with the style i have defined (upper) and a default titlebar (lower). How can I remove the default titlebar?
Important code:
App.xaml.cs:
MainPage = new NavigationPage(new AppShell());
Page1:
<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:viewModels="clr-namespace:foo"
xmlns:converters="clr-namespace:foo.Converters"
x:Class="foo.MainPage"
NavigationPage.HasBackButton="False"
Title="foo"
Loaded="ContentPage_Loaded">
-- Content --
</ContentPage>
Page2:
<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
x:Class="foo.Views.fooPage"
Title="foo">
-- Content --
</ContentPage>
NavigationbarStyle:
<ResourceDictionary xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
x:Class="foo.Resources.Styles.NavigationbarStyle">
<Style TargetType="NavigationPage">
<Setter Property="BarBackground" Value="{DynamicResource NavigationBarBackgroundColor}"/>
<Setter Property="BarTextColor" Value="White"/>
</Style>
</ResourceDictionary>
AppShell (more tabs are added later on):
<Shell
x:Class="foo.AppShell"
xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:local="clr-namespace:foo"
xmlns:views="clr-namespace:foo.Views"
Shell.FlyoutBehavior="Disabled">
<TabBar x:Name="MainTabBar">
<ShellContent Title="Home"
Icon="alert_icon_2_neg.png"
ContentTemplate="{DataTemplate views:StartPage}">
</ShellContent>
</TabBar>
</Shell>