Legend widget doesn't show the legend of result map service

[CocoZhu]

In web appbuilder, legend widget works fine with map service.

Now I have a gp service, which creates a categorical raster. I can see its legend at server. I can add the raster as a result map service to client with Javascript API. But there is no legend for the result in legend widget.

I'm wondering this is an issue of legend widget, or I should take some special steps to make the result map service come along with its legend.

Any clue will be appreciated very much.

[AlexisGreen]

I have the same issue when I load my geoprocessing service into Web Appbuilder.  I configured the GP service to return a result map service, and while the map service is displayed in my Web Appbuilder app, there is no legend defining the symbology of the map service.  Have you found any answer or workaround to this problem?