iOS 4.0.1 "fast app switching" behavior in simulator vs device (iPhone 4)

I'm testing an iPhone app in both the simulator (XCode 3.2.3, iPhone SDK 4.0.1) and on the device (iPhone 4 and iOS 4.0.1). The simulator exhibits the expected "fast app switching" behavior while the device doe开发者_StackOverflow社区s not.

Simulator:

• click home button while app is running => go back to home screen
• click the app icon => app resumes where it left-off (app does not restart)

Device

• click home button while app is running => go back to home screen
• click the app icon => app restarts (does not resume from the user quit)

Why is this happening?

Maybe your phone is low on memory.