DEAR PEOPLE FROM THE FUTURE: Here's what we've figured out so far???
I have created an ArcGISLocalFeatureLayer with a different spatial reference from the base layer, then I create a polyline that is added to the Graphics container of the layer.
As my data is in another spatial reference, I remove the layers from the map, change the spatial reference of the map and add the layers again.
Then I add the new layer (the one with the polyline)...at this moment the Graphics property onf the layer turns to 0, it just dissapear!!
maybe my code is haunted....
any suggestions??? where my polyline goes? why the polyline appear in the map (i can view the line in my screen) but not in the Graphics list