Mine does the same thing, and I thought the same thing. I can't find anything else on Google about it.
Also, it's not in iTunes. It's in Windows Explorer. Mine shows up as 52GB, but the additional space shows up as "used" space because the amount of free space is correct. I suppose Apple didn't get lazy and rebrand 64's as 32's in an effort to get supply ready for launch?
Actually you are right. It's in windows explorer. Glad someone. Else has the same "issue".