Problem with navigation in Xamarin.Forms on IOS ?

Hi guys !
I have problem with navigation in Xamarin.Forms on IOS . I have PageA, from PageA I use PushModalAsync method to push PageB, from PageB I use PushModalAsync to push PageC. In PageC, I use PopModalAsync method to pop back PageB, on Android it worked fine as well but on IOS, Page C popped back to PageA instead of PageB ? Can any body could help me ?

Thank in advanced.