Using Sonar Artist. Here is what I am trying to accomplish. Piano vsti on a simple instrument track. Clone the track so that I can exchange the the instrument for a different piano vsti on the cloned track, and blend to taste.
A different DAW I was using did this exactly as described, however when I exchange the instrument on the cloned track in Sonar, Sonar changes both tracks to the new vsti. 
Am I missing something obvious? I confess to being a (m)idiot.

You either have a preference that allows the cloned tracks to mirror themselves. In other words, what ever changes are made to one, will happen to the other.  Or you just need to insert another instance of the soft synth.
 
CJ

Many ways to do things in Sonar. What you could do is ...
 
- Insert your new soft synth e.g,  as a simple instrument track.
- Select your clip(s) from your original track, e.g, by clicking in the clip header bar (at the top of the clip). (Shift-click on the first/last to select all in between, or less likely CTRL-click to select multiple non-adjoining clips).
- Hold CTRL and drag it/them to your new track. (CTRL will take a copy instead of moving the original clip(s)).

Yes. Record the track with one VSTi. Insert the 2nd VSTi and copy the midi to it.

Use ctrl + shift to preserve vertical alignment when copy/dragging

Thanks all. I'll give these suggestions a go.