Strange. How do you observe that/what do you see?
You need to use Xcode and have a
free developer account
1. Plug your iPhone into your Mac and fire up Xcode. Make sure the Facebook app is in the background
2. The Organizer window should pop up (if not, press Shift+Cmd+2), then select your iPhone and press "Use for Development"
3. Now go to Xcode > Open Developer Tool > Instruments
4. In Instruments, select Activity Monitor under iOS, and start recording