I'd like to apologize to all of you who took the time to respond. I've been out of pocket for a while and couldn't readily respond.
After reviewing your comments I went back and reworked my steps. Alas, operator error (read as nincompoopery) was in fact the culprit.
It seems to me that in the past when I have chosen the flat area clearance option my previous selection was used as a default and I have simply gone about my business. Now when I choose it there is nothing selected and the compute option is grayed out until something is selected. In short, it's working perfectly. I must have either mis- remembered or am completely mistaken. Both options are highly plausible.
Thanks so much for help and taking the time to respond. I appreciate it greatly and will try in the future to be a better forum attendee.