Comp not muting previous track

I'm using the latest version of Platinum.   Does any one know why - when I record a new take in comping mode the previous take is not muting?  This is what you would expect if I had it set to Sound-on-sound which I do not.    I've used the comping mode thousands of times since its introduction with relatively no issues. 
 
Did I accidentally hit a keystroke for a setting (that's happened before)?