Hi Scott,
The change you have noticed is a recent one. It applies to 7-Mode and cONTAP. From the Release Notes for 8.1.2...
"Beginning with Data ONTAP 8.1.2, Data ONTAP will, by default, automatically giveback to the partner after a takeover due to the partner panicking. This giveback can be disabled or reenabled using the new -auto-giveback-after-panic parameter of the storage failover modify command .The automatic giveback reduces the amount of time the HA pair operates with a node in takeover mode."
This change was implemted after analysing support cases and observing customer experiences of takeover / giveback events.