here's how i fix this issue, as it also happens on the iphone4.....
1. unlock your iphone
2. open the photo app
3. plug your phone into computer/itunes and click "sync" while the photo app is open
4. after phone is done syncing, you should see the battery charge icon on your iphone, move the lock slider to the right to "unlock"
5. you should see a white screen with grey picture frames on your screen and the words "updating your photo albums" (or something along those lines)
if it still is jacked up, just re-click the sync button in itunes.
the key is in step 2. make sure you have the photo app OPEN before you sync.