Not knowing at all what vinegar is actually made from and only knowing we have to go get more of it around Passover, I am not sure if it is the fermentation method or what is being fermented that's the problem. If it is made from fermenting wheat (or rye or other grain) in some way, then I am guessing that it's why we have to change it.

Also it tastes different (and makes the ketchup taste funny). So I don't know exactly what makes it different, only that it is. And was throwing it out there as a Helpful Suggestion.