I have found a bug with layers in Argo, it seems to be possible for objects to be assigned to more than one layer.
I created a couple of layers, 'Spot' and 'Wash'. Put some spots into the Spot layer, then added some washes whilst the Spot layer was still selected. Then I selected all the washes and changed their layer to Wash. Now when you click the red ? it will list both layers even when you only have one fixture selected. If you try selecting all by layer it will select all fixtures in both layers.