The following interface messages seem to be treated as raw HTML in MobileFrontend, but aren't listed in RawHtmlMessages:
mobile-frontend-categories-add-heading
mobile-frontend-categories-add-wait
mobile-frontend-categories-heading
mobile-frontend-changeslist-nocomment
mobile-frontend-contributions-404-desc
mobile-frontend-editor-anonwarning
mobile-frontend-editor-editing-page
mobile-frontend-editor-licensing-with-terms
mobile-frontend-editor-previewing-page
mobile-frontend-editor-summary
mobile-frontend-editor-summary-request
mobile-frontend-editor-wait
mobile-frontend-talk-add-overlay-submit
mobile-frontend-talk-topic-wait
There are probably more. I created this list by adding an <img> to every single MediaWiki page corresponding to the MobileFrontend /i18n/en.json, randomly clicking on buttons in the mobile editor, then grepping apache logs for .jpg requests. I'm sure I haven't displayed everything, yet.
MobileFrontend may also be treating some non-MF interface messages as HTML; I haven't looked yet.