Minor Description
After reviewing QueryClient class, it appears that it is using the HttpClient and DataMapper defined on it instead of the same properties on the its base class, HttpServiceBase. Note that QueryClient.HttpClient and QueryClient.DataMapper are marked as obsolete.
Hmm, looking a bit deeper, QueryClient.DataMapper and QueryClient.HttpClient delegate to the base implementations, so not a huge deal. It does cause a compiler warning, however, which could be mitigated by disabling with #pragma.