[Unity4.3]After upgrade to Unity 4.3, It is slow when back from android activity

I created an activity extend UnityPlayerActivity , I called another activity out of my project and it do successfully.
When I press the back button, the activity in front of the screen destroyed painfully slow. It takes almost 5 second when the activity back call its' onResume method.
I have tested it in Unity 4.1.5, and It work crazily fast!
Anyone can tell me why?
Any help would be appreciated

 

Hi,

Not sure my problem is the same but with prime's 31 plugin after showing an admob interstital and going back to game i lost 30 FPS

I switched to chartboost ad (who i think dosen't "swap activity) and evevrything work well.

 

Not about admob, I just open an android activity , and escape from the activity. The acticity close too slow!