I have a set of two layers in my map, similar to the "Selection" example. When in SelectionOnly mode, no features are returned upon selection. In any other mode, any method of selection works just fine. Am I missing something? Is there anything specific to selectiononly mode with proxy pages that I need to know? I can't figure out why this is not working. Note that I am currently using the EditorWidget, though I saw the same behavior using the Editor tool. In other modes, I had it working with LayerIds set to the layer I wish to select or not specified at all.
I have tried adding the layers from the online selection example and that works just fine.
Thank you for reporting this bug. Editor.Select does not currently include support for ProxyUrl or Token. What you can do is create a SpatialQuery and set query.ProxyUrl to your featureLayer.ProxyUrl. You can refer to this sample: http://help.arcgis.com/en/webapi/silverlight/samples/start.htm#SpatialQuery