If I'm in a 3D view and want to attach some interior walls to the roof, I used to temp hide the roof - then select the walls - select attach top- then reset temp hide - then select the roof. I always used this method in Revit 8/8.1 and probably previous releases, but now in r9 this doesn't seem to be possible? What happened here? It seems the walls get unselected as soon as I touch the hide/isolate button.