JohnInKansas told me (in the course of a long and informative post):

If you've removed Real Player, or any other program(s) that might have made registry entries, by just deleting the folders instead of going through Add/Remove Programs or using an uninstall program specific to what you're removing, Registry Mechanic would be likely to find something to correct.

I went through Add/Remove. I've been the "just delete" route in the past, to my sorrow.

Having run Norton AV Full System Scan last night (about three hours), with nothing found, this morning I tried again multiple times to trigger the offensive behavior, and have not been able to. I'm fairly sure that getting RealPlayer off my machine has fixed it.

I just now downloaded Real Alternative, and will give it a try.

I thank everyone for their input.

Dave Oesterreich