As a real estate agent, this is not my field. However, this question had come up in the past with a client of mine and it is my understanding that some liens are attached to the person. So even though that person sells the house, he will still be responsible for it. Other liens are attached to the property which means that after a transfer of ownership, the NEW owners would be responsible for it because they are now the owners of that property.
Think of the home as collateral, and that is what the lien is being attached to. If the home is being disposed of in a bankruptcy, then the lien can no longer be placed on the home since it is separated from the owner in a bankruptcy. A good settlement attorney will be able to protect you on the purchase, and although people feel it is a scam, title insurance is a must in this situation. I can assure you that you feel it is a scam until you need it...just like all insurance! If the seller can not provide a clear title on the property, then there are few lenders who will allow for a loan to be placed on it.
Just make sure you have a good settlement group.
Basically a lien can be attached to a property or person. If attached to a property, then that lien has to be satisfied before the title can transfer free and clear to another owner.
Since the lien in question won't attach to the property, then the property can be sold without the new buyer needing to satisfy that lien.