Volvo's of the past use to do this, which I thought was a great idea, but no longer, at least in the S60. The recirculation timer only turns off recirculation mode after a certain length of time to prevent fogging or stale air. Kind of a useless feature but I'm glad I can turn that function off.Could be the HVAC blower running. I've got mine set to continue to run after ignition is shut off to help prevent a stinky A/C duct system.
My Car/Settings/Climate Settings/Recirculation Timer