i hear that there is something to do with pim backup corrupting some of the contact files, even if you backed them up at one time with pim and use active synce now just throwing my thoughts as they pop in my head so i am not a pro just trying to help
so i would say try entering a few contacts on a fresh flash, and see if the issue persist, or flash stock, hard reset, load newest build let customizations go thru, wipe device, load contacs and see if that helps
roger