Not certain, but I'd try this...
You've probably got a couple of corrupt preference files.
Safe Boot from the HD, (holding Shift key down at bootup), run Disk Utility in Applications>Utilities, then highlight your drive, click on Repair Permissions...
where 'xxx' is a 12 digit (hexadecimal) numeric string.
This will reset your Menu Bar to the default, you'll need to go through System Preferences to reset the ones you need. (If they are already checked, uncheck them first and then recheck them).
Thanks for taking the time to provide such a detailed reply.
The issue had been occuring for the last several days, but the day before I received your reply, I had a Software Update come through. I don't recall what programs required updating, but after the update the problem went away.
As an exercise in trashing Preference Files, I will follow your instructions anyway.