Why would my app is perfectly working with iOS 8 but not iOS 7 with some images

Hi,

I'm currently working on a Xamarin.Forms App that used TabbedPage.
For iOS 8.x, Images for Tab in my TabbedPage are perfectly displayed

I Also have I similar problem for my custom renderer Map

Here some screenshot for better understanding.

So, Anyone know why I could have my images not displayed for iOS 7 ?

Regards,

Cyril