I've been experiencing the same the same exact issue. Images inserted into the HTML view via Media Manager with 'HTML Editor Syntax Highlighter' active just don't show up. Visual editor works okay, but not HTML. I've taken to copying other image snippets pasting them into HTML editor, going into Media Manager copying the url of the image I want, then pasting that into the appropriate place. That's no way to work! It's easier to just disable your plugin altogether.
Wish WordPress developers would just include the functionality of your plugin into a new update of WordPress. So many people spend so much time in HTML ... it would make life so much easier.