Contacts missing after upgrade

[svaldesm]

I had an iPhone 4 running on 4.3.3. Not jailbroken or unlocked.
Updated to 5.1 with the last iTunes. Before updating, iTunes automatically made a backup of my data.
After updating, the restore progress started, and everything went back to normal, except my contacts.

It's weird because when I open the phone app, it shows for a few moments the names, but then only the numbers. The same happens with SMS and Whatsapp.
I thought iTunes didn't backup my contacts, but with a program found on the internet, I was able to check what was on the backup, and all the contacts are there (in fact, I could only export 4 of them because only the paid version allows you to export everything, but the thing's that they're there).

So, the question is, what should I do? I tried rebooting, restoring again, turning off iCloud (even closing the account) even though I hadn't saved any contact in there, and many other things. There are some alternatives that involve jailbreaking and some pro staff, but I think the problem is more basic and was hoping that any of you would guide me.

Thanks a lot in advance,

 

[lelisa13p]

Subscribing to this thread because the same thing happened to my sister's iPhone 4s when she upgraded. She ended up having to reenter all of her Contacts. She was not happy.

OTOH, my upgrades on iPhone 4 and iPad 1 went perfectly. We can't figure out why the difference between her experience and mine.

 

[Arelunde]

OP - do you have your contacts in iCloud or something like Gmail?

If it's Gmail and iCloud is "fetching" the data, this may be the problem. When I updated to iOS5, I was using Gmail for email, contacts and calendar. There were problems instantly. Contacts showed up a total mess with duplicates, missing listings, old data, etc. I tried to clean it up, but the final straw was when the Google calendar showed up blank.

I figured if I had to rebuild the calendar, I would use iCloud for all ... email, contacts and calendar. So far, it's gone very smoothly. Was a PITA to do, but worth the effort.