Well, this has been disturbing. I just opened Calibre and checked for "bugs" in my fixed layout EPUB. The resulting list is long. Apparently, there are many "CSS: Property: Unknown Property name. [1;65: -webkit-transform-origin] problems. When I click on the first one, the editor displays the XHTML file and highlights the problem area:
<div style="width:1520px;height:480px;position:absolute ;top:4.14px;left:0px;-webkit-transform-origin: 0% 0%; -webkit-transform: rotate(0deg) scale(0.05);transform-origin: 0% 0%; transform: rotate(0deg) scale(0.05);">
This is disconcerting from someone who has never written code and doesn't know much about HTML. I have no idea how identify or fix this problem.