You’re right, I was not clear in my explanation or terminology. When I said layer 0 I should have meant what I call “loose geometry”, which to me is geometry which has not been made into a group or component. Forget the reference to layer 0, as I know that has no bearing on the issue. Intersecting geometry that is either “loose” or within the same entity breaks up the entity into new parts–which then are not as easily editable as the knowledge base suggests.
Secondly, I often create a plane or face as a “workshop” floor to aid in moving around my models–especially for zoom. When trying to grab a hold of the arc for editing, the move tool instead grabbed the workshop floor face–though I didn’t know that because this face extended beyond my screen working area.
Another big revelation was provided earlier by john who specified to use the move tool without first selecting the arc entity. I’ve never seen that condition before. Wish that had been made abundantly clear in the arc edit tool knowledge base.
Thanks for all your help!