Not too surprising.
The same chassis is probably used for all FR's 831 models.
The rear kitchen hangs a fair amount of weight at the end of a lever far from the fulcrum (IE: tires).
A bit of flex is not surprising.
Enough to jam the door might be of concern though......as you mentioned, probably just a casualty of light weight/cost cutting/profit chasing bean counters....
2011 Flagstaff Classic Superlight 831RLBSS "Atrium slide"
Husky Centerline Hitch
1998 GMC Sierra SLE K2500 6.5 Turbo Diesel