Thanks Sheldon.

The only issue I have is with your comment:

"The worst-case scenario is that you will be riding along with the bike in its highest gear (large front, small rear) and then for some bizarre reason shift down in front before downshifting in the back. (There is no shift pattern in which it is reasonable to shift in this sequence.)"

I assume you are speaking of road bikes specifically? On MTB's, it is quite common (ie. not "bizarre" at all) to shift from the big chainwheel to the middle chainwheel when in the highest (smallest) cog on the back, then downshift through the gears out back.