在ChatActivity按返回键时，环信SDK会自动清除信息，请问如何解决

ChatActivity就从Demo拿过来的，没做太大的修改，在按返回键时会自动删除数据库的信息，现在想要做到在退出ChatActivity时，不删除聊天信息，该如何解决呢？
在进入ChatActivity和退出ChatActivity时日志如下：
07-21 12:52:44.227: D/EMDBManager(7334): add converstion with:1437118186993
07-21 12:52:44.241: D/EMDBManager(7334): save msg to db
07-21 12:52:44.242: D/EMDBManager(7334): add converstion with:1437118186993
07-21 12:52:49.551: D/EMDBManager(7334): add converstion with:1437118186993
07-21 12:52:49.558: D/EMDBManager(7334): save msg to db
07-21 12:52:49.563: D/EMDBManager(7334): add converstion with:1437118186993
07-21 12:52:53.856: D/EMDBManager(7334): delete group messages with:1437118186993 return:2
07-21 12:52:54.568: D/EMDBManager(7334): delete chatroom with:1437118186993 return:1
07-21 12:52:54.584: D/EMDBManager(7334): delete group messages with:1437118186993 return:0