I have now same result with Open Street Map
AGSOpenStreetMapLayer *osLyr = [AGSOpenStreetMapLayer openStreetMapLayer];
[self.mapView addMapLayer:osLyr withName:@"OpenStreetMap Layer"];
AGSSpatialReference *sr = [AGSSpatialReference spatialReferenceWithWKID:102100];
AGSEnvelope *env = [AGSEnvelope envelopeWithXmin:
9183090.953483 ymin:7363658.125409// correct = 7301109.281239
xmax:9301013.541211
ymax:7364392.063907// correct = 7454408.645285
spatialReference:sr];
[self.mapView zoomToEnvelope:env animated:YES];
If I insert incorrect ymin and ymax values (ymin is too near from ymax) then map is drawn correctly (without flattening).