Posted by Aikonoklast
Many people seem to be experiencing this. I haven't nailed down the cause but it seems that it happens only when I use the Xtndconnect sync software.
What are your observations?
Posted by Antanas
1. You have old software. 2. Several SIM cards. So make master reset and upgrade
Posted by georgied
Has anyone ever had numbers disappear from the position list but remain in the phonebook?
This happened to me a couple of weeks ago, and when I got a call from someone who disappeared from just the position list it did't recognise them from my phone book! 
Very annoying! 
The only way I got round it was a master reset and loading the phone book again.
Anyone else ever had this problem?
Posted by Cophia
Yes, that happened to me once. A master reset and reload of my data from my PC was the way I fixed it too. Hasn't happened since.
Posted by adamrj
Well the numbers disappeared from my phone book, but were still in there although I couldn't see them. I sorted it by taking off the battery while the phone was on, then putting it back and switching on (thanks to decoy7).
Adam