The next and previous buttons trigger javascript functions showNextMediaObject() and showPrevMediaObject(). They are defined in mediaobjectview.debug.js (debug version) and mediaobjectview.js (minified version). Can you add a line of code to these that call your own javascript?
If that seems daunting, the only other thing I can think of is to modify those functions to force the browser to do a full page load for the updated media object. You can use code like this:
window.location = getPermalink(moid);
For example, you could add this line this near the end of showNextMediaObject() and showPrevMediaObject() - maybe just before the if block that calls refreshMetadata(). I haven't tested this...
Roger Martin
Creator and Lead Developer of Gallery Server Pro