Someone found the source code for the driver that's caused the problem in the Zune 30, from the Freescale website (http://pastie.org/349916)
//Copyright (c) Microsoft Corporation. All rights reserved.
//Copyright (C) 2004-2007, Freescale Semiconductor, Inc. All Rights Reserved.
//PQOAL Real-time clock (RTC) routines for the MC13783 PMIC RTC.
It goes into an infinite loop at boot because of an off by one error!
It looks like the original report of the driver source discovery, with more detailed information, can be found here.