An update probably resets a lot of defaults, if not all of them, this is to make the transition of updating your device easier and cause less issues for the user.
Unfortunately this will probably always be something that happens, it just prevents bugs/issues when an update is pushed through without a factory reset, which are what updates for android OTA do, which sometimes is frowned upon just because factory resetting your device after an update makes sure your phone doesn't have any issues post-update.
Honestly a way around it might be getting a custom contacts application and using that to set custom defaults and such for specific contacts. That way this information is saved in a downloaded application and not one that is standard for your device.