It's an odd day when the best way to find the answer to a Marantz or Pronto problem is to search the site for the word "prick." But it worked!
I did not remember that the calibration process on the RC5400 required touching all four corners, so when I touched only three of them and the process appeared to move forward to an announcement of failure, it still seemed as though the remote was registering all of the touches.
The pin prick method cured it. The longest part of the process was finding the method. If you need it, you'd best search for the word "prick" and designate the search to return answers as posts, not threads. The thread gives you twenty-four pages to go through. If you want to just go read all of them, they are at
[Link: remotecentral.com]And as someone said back in 2008,
Thanks to bongiornoa, PeraV, fransvdmb, jw2k_fr, and many others for discovering and documenting this fix!
And more thanks to Lyndel for passing this on to me.