yes, prior debts. The Alan Dean Foster case alleges that they stopped paying royalties on newly generated income.
Because it seems to be a touchy and confusing subject I will again preface this statement by saying that this is speculation on my part as much as assuming that Disney is guilty is speculation on the part of anyone else.
In this thread we are discussing prior debts and ongoing royalties (despite neither being what the actual case is about). Both of these things are covered by whatever contract was entered into by the IP holder and whoever they did work with. The contract can say "I owe you $500" or "I owe you $1 per book sold". Really it does not matter in the slightest if these are existing debts on the books or potential future debts when it comes to the sale of the IP. They are both considered liabilities.
If the purchaser does not want to acquire the liabilities then they don't need to. No law says that a exchange of property must be done whole or not at all. If you purchase a car from your neighbor but they haven't finished paying it off themselves you have a choice. You can either agree to the terms of the contract they signed with the dealership and deal with whatever potentially bad agreement they signed or you can tell the seller that you will buy the car once they complete their transaction with the dealership and you don't need to deal with that liability any longer. You can attempt to do this with any liability during a negotiation. If Disney does not want to pay royalties to people it never hired then they can ask for that and its the sellers job to go to the people they hired and pay them off so the deal is as clean as the buyer is comfortable with.
Its really wild to think that this is not a pretty obvious negotiation measure for most. Here is one last crazy hypothetical situation to maybe illustrate it.
You find a car for sale. Its your dream car and everything is absolutely perfect with it. In fact you think you could use it to make some cash on the side at car shows or something. You meet up with the seller and he says "Yeah I hate to see it go. One thing you should know is that I still owe the bodyshop $5000 on the fantastic work they did. Also there is this old guy who I made this deal with. He was the one who sold me the car and part of our deal was that I would let him drive it to BINGO the first sunday of each month. Of course now you would be responsible for paying back the shop and letting the old guy take the car out. That's cool right?'
At this point any normal person would say no. You would want them to pay off their debt to the body shop and talk to this old guy about how he wasn't going anywhere in the car anymore. If this man wants your money and wants to make this sale then those are your very reasonable conditions. Maybe the seller refuses to do either and then I guess the deal does not happen. Lets think positive and say the deal happens. The seller pays off the debt and agrees to handle the old guy. You drive off happy and the previous owner has a wallet full of cash. A few months later this old guy starts banging on your door. He's yelling at you because you haven't been lending him the car. He's outraged. How could you do this to a poor old man? Maybe he will go to the media about how this young hotshot in his shiny new car is breaking the promises made to a frail old man.
So whos at fault here? Can the car simply never be sold without the loose end of the old man? When the old man dies can his family bang on your door asking for rides? Is it fair for the buyer to be painted as the villian for just wanting a clean transaction and assuming that the previous owner would settle up with his promises?
Contracts and their contents are important. Those that say "I don't care", "Too bad for them", and "It doesn't matter what the contract says" are blessed to have never been on the butt end of legal disagreement involving contract or tort law.