I'm seeing duplicate popups returned by the .NET SDK (100.0) release:
Using the same web map, an identify on a feature using ESRI's default JS webmap viewer returns a single popup as demonstrated in this screen grab.
Clicking on the same feature in a sample WPF app (using the IdentifyLayersAsync() method) returns an IdentifyLayerResult which contains two popups, which appear to be duplicates. Notice matching objectids written to the VS output window:
I've checked the underlying data that drives the map service and there isn't anything weird like duplicate features in the feature class. Regardless the JS API seems to be doing it right. I'm stumped. The web map is linked above and the sample WPF app is attached for Esri's convenience.
Thanks in advance.