Please add RotationTransform for MapItemsControl at OverheadMap.
Becouse name of the MapShape rotation with map too.
change xaml
<DataTemplate x:Key="MapShape">
<maps:Pushpin Location="{Binding Location}" Content="{Binding Content}" >
<maps:Pushpin.RenderTransform>
<RotateTransform Angle="{Binding Tag, ElementName=Map,Converter={StaticResource AddMinusConverter}}" CenterY="61" />
</maps:Pushpin.RenderTransform>
</maps:Pushpin>
</DataTemplate>