I've had Beta 5 installed since it came out without this issue, but today I checked iTunes and it's asking me to set up as a new device or restore. Tried everything I can think of (aside from actually doing one of those two things), and nothing fixes it. I can't turn off WIFI sync in iTunes because I can't get past the "set up as new device" screen. There's no way to turn off WIFI sync on the phone itself, but I tried just turning off WIFI itself and that didn't fix the problem.
I can still back up to iCloud and I can force a manual sync by going into WIFI Sync on the phone. But in iTunes, it shows the "set up as new device" and I can't change anything.
Since Beta 6 is coming out soon, I'm not going to restore or set up as a new device for now. But if anyone comes up with another solution for this problem, I'm all ears! ;-)