automatic wifi sync not happening

i'm on a black macbook running the most current versions of max os, itunes, and ios. my phone is the iphone 4.

i am not having the problem of wifi syncing as a whole because i can initiate the sync from my phone in the settings, but it is supposed to just start syncing when you plug it into a power source, right? that's what it is not doing for me. clearly my computer and my phone are communicating. the wifi sync can be done if i click "sync now" but it does not automatically start a sync when i plug it in. ideas? suggestions?

thanks!

sam