I do wonder if the reason there is so much push back on this issue is the fact that perhaps all of the ECR 327's are like this. If that were the case one would think more complaints would be showing up on Google searches, but I could see the possibility that most users of these jacks don't care that much if the acceleration is choppy...crashing into pallets of produce or whatever and running at breakneck speed might not matter that much to them.
If the company is managed using the "meet your profit objective, no excuses", then ignoring the problem may be the Veeps only way to get his/her bonus.
Your approach to post this on other forums, as many as possible, that folks might check before making the mistake of buying a Jungheinrich will at least give you psychic comfort.
I do think you should elevate this with a letter, using the words "sudden unintended acceleration", emphasizing that such a design or manufacturing flaw could result in death, serious injury, or significant property loss. At the very least, emphasize that the flaw makes the unit useless for it's intended purpose. Send it to the distributor, the US HQ, and to the German HQ (nice if you can get it translated into good old Deutsch.) Emphasize that the company appears to be ignoring their warranty. You may wish to emphasize the publicity that this is getting on the many forums you are posting the story on, and that the exposure that design defects, poor (nonexistent) customer service, and failure to honor the warrantee may be having on sales. I'd mention the Chevy Cobalt design defect.
I would CC Legal affairs in the US office. May be worth writing the letter up, and seeing if your lawyer will put it on his letterhead for a small fee. Sorry to say that this gets folks off top dead center sometimes.
But this does sound like "wanton indifference" to a dangerous design or manufacturing defect that causes sudden, unintended acceleration of a a device that may weigh over 6000 lbs. Its nuts, and bad business, for them to ignore it.