I created a hosted feature layer with some ploygons and a few columns in it. The polygons are projected to web mercator. I added the layer to a webmap and it performs as I would expect, but when I load the webmap in my .NET application, the layer doesn't draw when I pan around. I checked out the network traffic with Fiddler and I found that it was giving the service an envelope with only xmin, ymin, xmax, and ymax to intersect with. It also defined the input spatial reference as 3857, which should be correct. When I put the same parameters into the REST query page in my web browser, I get no results. However, when I change the input spatial reference to 102100, it gets the correct results.
Then, I checked what was going on in ArcGIS Online by looking at the network traffic in the Chrome developer tools, and I found that it is sending different query parameters to the service. The big differences is that it defines the input spatial reference as 102100 and it also defines the spatial reference in the envelope object that it does an intersect with.
Is there any way that I can force the ArcGIS Runtime to use 102100 rather than 3857 and why does it matter, given that these both represent web mercator? I should also mention that the JSON definition of the hosted feature service says that the wkid is 102100.