This is a strange one indeed. And a little worrisome that it's on some but not all pages. Can you detect a pattern?
Between 8.x and 9.x, there was a fix concerning HTML entities. This solves the false positives we used to get in diffs. Ref: http://tiki.org/ReleaseNotes9.0#HTML_entities
Do you think you could have it investigated/resolved the same way you did for Flagged revision reports?