I got the same Problem, that you have with the Java Client, with the .NET client.
After contacting Google support, they told me that the Contacts arbitrary XML data which is in an Property element cannot be parsed within my version of GData .
However, there is a time intensive workaround, by deleting and recreating Contacts, but thats probably not what you are looking for, me either.
After switching to the Python implementation all works fine now.
Check out this Issue report Issue 361