Behind Obama's Puzzling Warning About Flynn

Why did outgoing President Trump make it a priority to warn incoming President Trump against hiring General Flynn to be National Security Advisor?     

Trump told aide Hope Hicks that he was bewildered by the president’s warning. Of all the important things Obama could have discussed with him, the outgoing commander in chief wanted to talk about Michael Flynn.    Obviously, Barack Obama revealed his great hatred for General Flynn to President Trump during their first private meeting.    (snip)
Flynn not only made it clear that he wanted to undo the Iran Deal, he also broadcast his determination to find the documents detailing the secret deals between Obama and Iran, and to publicize them.

Flynn would undo Obama's legacy move and publicize secret deals with Iran.  How cynical is that?