Purchased a home at foreclosure auction?

We purchased a home in a foreclosure auction in Machusetts. Right before closing we heard that the foreclosed owner claims that there has been a bogus Power of Attorney for the mortgage that was foreclosed on. I checked the paper at the registry and it looks like instead of the actual owner somebody else has signed with POA next to their name. This doent is notarized. However the notary says that the actual owner is at presence. Anyways, they're getting the house back with a claim that the signer on the $360K mortgage is a fraudulent person. How can this happen?