Xamarin.Forms iOS Label word wrap problem ?

First line appears immediately but the results of next calls like

  void button_2_Clicked(object sender,EventArgs e)
  {
   bottom_label.Text+="Hello, Forms!\n";
  }

appear with some big delay, after many clicks of the button suddenly appear all that "Hello, Forms!".

This happens on simulator at iOS on iPad 2 and Phone 4.

It seems like there is no word wrap at all initially and then it decides to switch into that mode and does that with some delay.

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
                       xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
                       x:Class="test_cs_mobile_xamarin.main_page">
   <StackLayout>
      <Frame x:Name="top_frame" HasShadow="true" OutlineColor="Green" Padding="5,5,5,5" VerticalOptions = "FillAndExpand">
         <ScrollView  x:Name="top_scroll_view" VerticalOptions = "FillAndExpand">
            <Grid x:Name="top_grid" VerticalOptions = "FillAndExpand">
               <Grid.Children>
               </Grid.Children>
            </Grid>
         </ScrollView>
      </Frame>
      <Frame x:Name="bottom_frame" HasShadow="true" OutlineColor="Green" Padding="5,5,5,5" VerticalOptions = "FillAndExpand">
         <ScrollView x:Name="bottom_scroll_view" VerticalOptions = "FillAndExpand">
            <Label  Text="..." XAlign="Start" YAlign="Start" VerticalOptions="FillAndExpand" HorizontalOptions="FillAndExpand" x:Name="bottom_label" LineBreakMode="WordWrap" />
         </ScrollView>
      </Frame>
      <StackLayout x:Name="bottom_stack_layout" Orientation="Horizontal">
         <Button Text="Add 1" x:Name="button_1"></Button>
         <Button Text="Add 2" x:Name="button_2"></Button>
         <Button Text="http" x:Name="button_3"></Button>
         <Button Text="http 1" x:Name="button_4"></Button>
      </StackLayout>
   </StackLayout>