Default [Q] Issue with Assist Driving text messaging

The "Quick Reply" feature doesn't seem to work. No problem with the phone going into driving mode, speaking the name of who is texting as well as the text content, but the automated quick reply message doesn't get sent. On KitKat, using stock Messaging app. Location services seems to be active. Tried clearing Assist cache (and in fact, un and reinstalled Assist) no joy.

Am I missing something operationally?

Thanks in advance.