UPDATE on this issue in case others are experiencing the same thing.
- I contacted Adobe chat help about this issue.
- The tech support person accessed my PC virtually, saw the issue and tried a few things to fix it. He was not able to rectify the problem.
- He then checked and was able to reproduce the problem on a computer in his office, so it's not specific to my PC alone.
- He is now escalating the matter to the Engineering team.
- It could be - probably is - a bug. (I use Win 7 in case that's relevant).
C