05-02-2013 07:23 PM - edited 05-02-2013 07:57 PM
When writing contacts, try specifying an arbitrary account name/type. If you see a "null" account on your device, delete it. There is a bug where it won't sync if the account name/type is null (or if the "null" account still exists). Apparently they've fixed it, but it didn't make it into the 10.1 build.