They make sure to specify any ballast in the bullet point right above it, but then they forgot to put that in the second one even though you're saying it's the weight they're worried about? Come on man get serious.
If it were strictly a weight problem, they'd have mentioned it. It's a liquid sloshing concern. As in: the tractor gets a bit wiggly because you're operating across a grade, the ballast sloshes to one side and suddenly it's not just wiggly, it's going over.
As far as the rear end thing, when people start posting threads about their rear casting cracking because they jacked their tractor up, then I'll eat crow. Totally ridiculous.