web request fails after setting preferIpv6 to true

Hi

I am using chilkat v9.5.0.51 Mono on Mac, Xamarin iOS & Android. After setting preferIpv6 to true on my Http object, some servers fail to be requested, for instance:

http://nominatim.openstreetmap.org/search?q=sabah&format=xml&limit=20

https://maps.googleapis.com/maps/api/staticmap?center=34.2065687282483,-117.859450371377&zoom=16&size=638x667&sensor=true&format=png&maptype=hybrid

If preferIpv6 is false, these requests work fine. Is it a server issue? Can I fix it on the client side?

Thanks Guillaume