I've noticed the IPTC Contact information is getting wiped out in the image file upon a write sync. PSU does not lose the data upon a subsequent read because it appears to be reading and writing to/from the Iptc4xmpCore:CreatorContactInfo struct. I was able to observe this from Adobe Bridge CS6 which looks at the non-xmp IPTC Contact info in its metadata panel. PSU does not appear to be deleting any of the other IPTC info, just the Contact.
Dan