basically we need to take a look the debug trace. please take these steps:
1. follow instructions here to patch build 1278.
Single file patch for 1278 users
2. go to yahoo account setup page in desktop, and check the box at the bottom of the page that says "Enable debug trace".
3. do a sync by clicking "Send/Receive" to reproduce what the problem is. The debug trace will go into <install>/log/zdesktop.out
4. file a bug with to describe what you expect to happen after the sync and what actually happens. attach the zdesktop.out trace to the bug.
Thanks!