WPF - "g" is cut off sometimes - wpf

Question

I have a combobox in which I display simple strings. At some point this looks like the following:
This is ok. now ein scroll down one step:
Now the "g" is cut off at the bottom. What I have tried so far: Set the height property explicit to Auto. Changing Padding and Margin. Nothing worked. Had some of you the same problem or any suggestions what I could try?
EDIT
Here the related XAML:
<Style x:Key="GraphicEditorInplaceLabelEditStyle">
<Setter Property="ComboBox.Focusable" Value="True"/>
<Setter Property="ComboBox.IsEditable" Value="True"/>
<Setter Property="ComboBox.IsReadOnly" Value="False"/>
<Setter Property="ComboBox.IsTextSearchEnabled" Value="True"/>
<!--Use Separators for empty entries-->
<Setter Property="ComboBox.ItemContainerStyle">
<Setter.Value>
<Style TargetType="{x:Type ComboBoxItem}" BasedOn="{StaticResource {x:Type ComboBoxItem}}">
<Style.Triggers>
<DataTrigger Binding="{Binding}" Value="">
<Setter Property="IsEnabled" Value="False"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type ComboBoxItem}">
<Separator HorizontalAlignment="Stretch"/>
</ControlTemplate>
</Setter.Value>
</Setter>
</DataTrigger>
</Style.Triggers>
</Style>
</Setter.Value>
</Setter>
<Setter Property="ComboBox.Template">
<Setter.Value>
<ControlTemplate TargetType="ComboBox">
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition></ColumnDefinition>
<ColumnDefinition></ColumnDefinition>
</Grid.ColumnDefinitions>
<Border Validation.ValidationAdornerSiteFor="{Binding RelativeSource={RelativeSource FindAncestor,AncestorType=ComboBox}}" Background="{StaticResource ComboBoxActiveBackgroundBrush}" BorderBrush="{StaticResource ComboBoxBorderBrush}" BorderThickness="1" CornerRadius="2">
<Grid>
<ContentPresenter Margin="3,3,3,3" Content="{TemplateBinding SelectionBoxItem}" ContentTemplate="{TemplateBinding SelectionBoxItemTemplate}" ContentTemplateSelector="{TemplateBinding ItemTemplateSelector}" HorizontalAlignment="Left" IsHitTestVisible="False" Name="ContentSite" VerticalAlignment="Center" />
<TextBlock Style="{x:Null}" x:Name="PART_TextBackground" Margin="3,3,3,3" Background="Transparent" Focusable="False" FontStyle="Italic" Foreground="LightGray" HorizontalAlignment="Left" VerticalAlignment="Center"/>
<TextBox Style="{x:Null}" x:Name="PART_EditableTextBox" Margin="3,3,3,3" Background="Transparent" Focusable="True" HorizontalAlignment="Left" IsReadOnly="{TemplateBinding IsReadOnly}" VerticalAlignment="Center" Visibility="Hidden">
<TextBox.Template>
<ControlTemplate TargetType="TextBox">
<Border x:Name="PART_ContentHost" Background="{TemplateBinding Background}" Focusable="False" />
</ControlTemplate>
</TextBox.Template>
</TextBox>
<Popup AllowsTransparency="True" Focusable="False" IsOpen="{TemplateBinding IsDropDownOpen}" Name="Popup" Placement="Bottom" PopupAnimation="Slide">
<Grid MaxHeight="{TemplateBinding MaxDropDownHeight}" MinWidth="{TemplateBinding ActualWidth}" Name="DropDown" SnapsToDevicePixels="True">
<Border x:Name="DropDownBorder" Background="{StaticResource ComboBoxActiveBackgroundBrush}" BorderBrush="{StaticResource ComboBoxBorderBrush}" BorderThickness="1" />
<ScrollViewer Margin="4,6,4,6" SnapsToDevicePixels="True" CanContentScroll="False">
<StackPanel KeyboardNavigation.DirectionalNavigation="Contained" IsItemsHost="True" />
</ScrollViewer>
</Grid>
</Popup>
</Grid>
</Border>
<ToggleButton Grid.Column="1" ClickMode="Press" Focusable="false" IsChecked="{Binding Path=IsDropDownOpen,Mode=TwoWay,RelativeSource={RelativeSource TemplatedParent}}" Name="ToggleButton" VerticalAlignment="Bottom">
<ToggleButton.Template>
<ControlTemplate TargetType="ToggleButton">
<Grid>
<Border x:Name="Border"
CornerRadius="2"
Background="{StaticResource ComboBoxActiveBackgroundBrush}"
BorderBrush="{StaticResource ComboBoxBorderBrush}"
BorderThickness="1"
Margin="0,0,0,0" />
<Rectangle x:Name="arrow"
Height="6"
Width="8"
HorizontalAlignment="Center"
VerticalAlignment="Center"
Margin="2"
Fill="{StaticResource ComboBoxArrowDownBrush}" />
</Grid>
<ControlTemplate.Triggers>
<Trigger Property="ToggleButton.IsMouseOver"
Value="true">
<Setter TargetName="Border"
Property="Background"
Value="{StaticResource ComboBoxMouseOverBackgroundBrush}" />
<Setter TargetName="arrow"
Property="Fill"
Value="{StaticResource ComboBoxArrowDownMouseOverBrush}"></Setter>
</Trigger>
<Trigger Property="ToggleButton.IsChecked"
Value="true">
<Setter TargetName="Border"
Property="Background"
Value="{StaticResource ComboBoxPressedBackgroundBrush}" />
<Setter Property="Fill"
TargetName="arrow"
Value="{StaticResource ComboBoxArrowUpBrush}" />
</Trigger>
<Trigger Property="IsEnabled"
Value="false">
<Setter TargetName="Border"
Property="Background"
Value="{StaticResource ComboBoxInactiveBackgroundBrush}" />
<Setter Property="Foreground"
Value="{StaticResource FontInactiveBrush}" />
<Setter Property="Fill"
TargetName="arrow"
Value="{StaticResource ComboBoxArrowDownInactiveBrush}" />
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</ToggleButton.Template>
<ToggleButton.RenderTransform>
<TranslateTransform X="-3" Y="0"></TranslateTransform>
</ToggleButton.RenderTransform>
</ToggleButton>
</Grid>
<ControlTemplate.Triggers>
<Trigger Property="HasItems" Value="false">
<Setter Property="Visibility" TargetName="ToggleButton" Value="Collapsed" />
</Trigger>
<Trigger Property="IsEnabled" Value="false">
<Setter Property="Foreground" Value="{StaticResource FontInactiveBrush}" />
</Trigger>
<Trigger Property="IsGrouping" Value="true">
<Setter Property="ScrollViewer.CanContentScroll" Value="false" />
</Trigger>
<Trigger Property="Popup.AllowsTransparency" SourceName="Popup" Value="true">
<Setter Property="CornerRadius" TargetName="DropDownBorder" Value="4" />
<Setter Property="Margin" TargetName="DropDownBorder" Value="0,2,0,0" />
</Trigger>
<Trigger Property="IsEditable" Value="true">
<Setter Property="IsTabStop" Value="false" />
<Setter Property="Visibility" TargetName="PART_EditableTextBox" Value="Visible" />
<Setter Property="Visibility" TargetName="ContentSite" Value="Hidden" />
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
I tried to change the padding/margin of the ComboBoxItem as well as the item host stackpanel.