Well, I got lucky with the above problem, which turned out to be an anomaly. All the problem behavior was with the 28mm Biogon, and so when I put on the 35 Planar... problem solved! I put both bodies side by side, lensless, and didn't see any difference in the lens connections. The 7 gold pins were all standing tall and shiny, but I brushed them lightly with an eraser tip. Same for the two lenses, examining their mounts.
So I put the 28mm back on and wandered around taking snapshots concentrating on sub-meter distances without any trouble at all. I can only guess that it was a glitch in the way the 28mm was seated on the camera that time. I'm happy as long as the problem stays gone!