iTunes not seeing my iPhone over Wifi

I posted this in the iPhone forum, but my guess is that the issue is more related to iTunes. So I am posting it here as well.

My iPhone doesn't show up in the sidebar of iTunes anymore, even though the iPhone is connected to and works over my wifi network. I had it set to sync over wifi and open iTunes when the iPhone was connected (e.g., checked these two boxes on the Summary Pane). But now, the phone doesn't show up at all. Oddly, my iPad shows and syncs fine. And, despite not being seen by iTuens, my iPhone is connected to my Wifi network and works fine.

I've tried unchecking and rechecking the box for wifi sync, but it doesn't hold. The phone will show up after I "reset" the check boxes with the phone attached to a cord and then disconnect the cord. After doing this, I can shut down iTunes and restart it, and the phone shows as being connected. Fine and good. But after I restart my iMac, the phone doesn't show anymore in iTunes. My guess is that this is an iTunes problem and not a problem with the wifi or the phone.

Any ideas on how to get my phone to stay showing in iTunes?