The ironic thing is that I appeared to have created the problem when I updated the export code to allow me to write unit tests for it. HTML export works fine in the test, but Tellico, the app, was setting the configuration wrong. All the articles I've read about there being no such thing as a harmless code change are true!
So, my apologies if you download Tellico, created a collection, tried to export your HTML page and promptly get a crash. We'll hire new Quality Assurance people immediately.