I had the same problem as all of you and solved it like that:
- Export all contacts as a yahoo csv file to my hard disk
- Delete all contacs in my yahoo account
- Delete all contacs in "Deleted contacts"
- Swich off syncing yahoo! contacts on iphone
- Import all contacts from my hard disk into the accout using the csv file
- Delete all lists and list suggestions which appear in the contact account window below "all contacts" and "shortcuts"
- Swich on syncing yahoo! contacts on iphone
- go to contact app and refresh contacts on top left
- be patient for a few minutes
having this done sync worked fine in both directions for about three months. about a week ago the phone started to go crazy:
when trying to create a new contact on my iphone by using a number of an incoming text message or call, the contact would stay in my iphone contact list for a few seconds. that the sync process with yahoo takes place, but yahoo doesn't seem to save the contact in it's account. so after a few seconds the new contact disappears from my iphone contact list (and has never appeared in yahoo).
a few days later, ALL my contacts were removed from my iphone contact list. they were still on may yahoo account. refreshing sync in the contact app and other things did not really work out (some contacts were synced, but not all of them). so i finally tried again the workaround described above and everything seems to work fine again. hope it lasts like that.
did you have similar problems during the last days? I guess that all these problems seem to have to do with an odd yahoo storage system which needs to be "cleaned up" from time to time.
my other settings:
- yahoo! mail pro
- european contacts with letters like ä ö ß
- iOS 5.1
- iphone 3gs
- "new method" (no carddav)
- all contacts are saved with first name and last name
- 300 + contacts; some with mail; some with up to 4 phone numbers; some mail, phone and other information