Never found what was wrong. What I did was rebuild the font, step by step copying over the glyphs and coding, watching for the error to pop up. It never did, so I believe that the original file must have been corrupted somehow during one of the Fontlab crashes. That is the only thing I can think of. Thank you to all who helped me, especially Peter Constable.
When I started my first text font, I just wanted to pay attention to the technical side of the work, so I purposefully made the outlines very ugly. My idea was to learn about character sets and open type without getting bogged down in the details.
In the end, I did notice that it actually shone at very small sizes. I did so many legibility tests, blurring the output and correcting for ambiguity, that it remains readable down to about 3pt. Not so much for screen, but a good xerox output was sharply readable.
So, I've done better since then. But you can't say it's not original.
I immediately thought of those modular type ornament blocks. I can only find one example right now. Sorry for the bad quality, my scanner is not working, but this is from The Lovell & Gibson Specimen book of 1847 (in reprint); if you look close you can see the individual blocks that it is built from.