Since Bank of America settled a Federal lawsuit some time ago (sorry, I forget the exact time frame) they were (are) required to settle on a large number of underwater second mortgage. I personally know several people who received letter from BofA canceling the second mortgage all together.
Admittedly, I have not heard of any loans being pulled back from a collection agency. It actually does not make sense, since collection accounts are usually "sold", so taking them back would not seem plausible. Unless, of course, the collection agency is a subsidiary of Bank of America.
Hope you will post your resolution, as it could help others understand the current (and ever changing) situation with second mortgages.
It is hard to make any guess without knowing all the facts. I recommend you call Bank of America and ask them. Escalate your question until someone can give you an answer. Personally, as a very general statement, I feel you are better off working through your debt with the bank than the collections agency.
Have you asked BoA? There are several possibilities, and getting out of collections is a good thing. They may have modified your second, written it off, forgiven it or just put you in good standing.
Congratulations, I suspect it's a good thing.