I had not noticed whether this seems to be mostly the rear kitchens or not. Interesting thought. If it is mostly rear kitchen models, then I'm at a loss as to why. The idea of a rear kitchen being heavier in the rear doesn't really hold water, although it sounds logical until you think about it. Our rear kitchen also has one of the heaviest pinweights, which means that much less on the axles. I assume the axles are mounted farther back to shift that weight to the front and to reduce unsprung weight (weight behind the axles). When we were looking at trading, back in 2002, I consulted a friend who was an RVCG member and had their touted manual. He told me the "book" said the 3295RK was, at that time, the most balanced of all Montanas, whatever that means.
It would be interesting to take a poll of those who have had this shackle problem and see if there is a trend to the rear kitchens or any other model or feature. Interesting thought. I suspect we'd find the common trait is miles. But that's just a guess.