Non-fatal build error in Runestone

/tmptfmu08cu.xml:54:75: error: element "image" not allowed here; expected the element end-tag, text or element "abbr", "acro", "ad", "alert", "am", "angles", "articletitle", "attr", "bc", "c", "ca", "cd", "chord", "copyleft", "copyright", "custom", "dataurl", "dblbrackets", "dblprime", "degree", "delete", "dl", "doubleflat", "doublesharp", "eg", "ellipsis", "em", "email", "etal", "etc", "fillin", "flat", "fn", "foreign", "icon", "idx", "ie", "init", "insert", "kbd", "langle", "latex", "ldblbracket", "lq", "lsq", "m", "md", "mdash", "midpoint", "minus", "n", "natural", "nb", "nbsp", "ndash", "notation", "obelus", "ol", "permille", "pf", "phonomark", "pilcrow", "plusminus", "pm", "prefigure", "pretext", "prime", "ps", "pubtitle", "q", "quantity", "rangle", "rdblbracket", "registered", "rq", "rsq", "scaledeg", "section-mark", "servicemark", "sharp", "solidus", "sq", "stale", "swungdash", "tag", "tage", "taxon", "term", "tex", "timeofday", "times", "timesignature", "today", "trademark", "ul", "url", "var", "viz", "vs", "webwork", "xelatex", "xetex" or "xref"

Start by reproducing the Runestone build that emits /tmptfmu08cu.xml:54:75 and inspect the source corresponding to that generated location. Determine why an image element appears where the validator rejects it; done means the build completes without this validation error.