Interesting question and good discussion.

I have zero experience with Massachusetts real estate and can only comment as this would affect Virginia property. 

You were right to report the judgment as a potential lien against the real estate. 

In my world, this would be a good judgment against the equitable interest of Joe Blow as to this property subject only to Joe Blow's obligation to pay the high bid price, any delinquent real estate tax, and any liens prior to the foreclosed trust. 

Absent anything to the contrary in the contract to purchase, equitable conversion took place on the signing of the contract to purchase at the auction.  Any increase in value or right to hold and convey transferred to Joe Blow and is subject to the blanket lien of the IRS.  The trustee/lender retained only legal title which, after the auction, was a personal property right. 

Obviously, there was record notice as to the IRS lien available.  My thoughts are the assignee took subject to the outstanding lien and is burdened by it.   

Good call on your part to report.  Well done.