The tension in the handlepost latch needs adjusting every so often so that there's no play. The loc-tite suggestion is just a means of avoiding having to adjust so often. Gradually with friction the handlepost latch surfaces will wear a little and some adjustment would have to be made to maintain tension, loc-tite or not. The (separate) issue with the handlepost rotating is just to do with the q/r clamp pressure. I don't have a problem with that on my VItesse (had plenty of other problems). The Dahon hype does rather suggest these are the most imaculately engineered bikes EVER, and they're not, but I don't think you've anything to worry about.